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The Linux Electronic Mail HOWTO Guylhem Aznar <guylhem at danmark.linux.eu.org> v2.0, January 1998 This document describes the setup, care and feeding of Electronic Mail (e-mail) under Linux. You need to read this if you plan to communi¡ cate locally or to remote sites via electronic mail. You probably do *not* need to read this document if don't exchange electronic mail with other users on your system or with other sites. 1. Introduction, copyright and standard disclaimer 1.1. Email and spamming First, convert all "at" in Emails address to "@". It's simple for humans, but not for bots searching the web to spam ; therefore it's enough to protect generous contributors from being spammed ! 1.2. Goals The intent of this document is to answer some of the questions and comments that appear to meet the definition of "frequently asked questions" about e-mail software under Linux in general and the version in the Linux Debian and RedHat distributions in particular. 1.3. New versions New versions of this document will be periodically posted to comp.os.linux.announce, comp.answers and mail.answers. They will also be added to the various anonymous ftp sites who archive such information including sunsite.unc.edu:/pub/Linux/docs/HOWTO. In addition, you should be generally able to find this document on the Linux WorldWideWeb home page at http://sunsite.unc.edu/mdw/linux.html. 1.4. Feedback I am interested in any feedback, positive or negative, regarding the content of this document via e-mail. Definitely contact me if you find errors or obvious omissions. I read, but do not necessarily respond to, all e-mail I receive. Requests for enhancements will be considered and acted upon based on that day's combination of available time, merit of the request and daily blood pressure :-) Flames will quietly go to /dev/null so don't bother. Feedback concerning the actual format of the document should go to the HOWTO coordinator : Greg Hankins (gregh at sunsite.unc.edu). 1.5. Copyright The Mail-HOWTO is copyrighted (c) 1998 Guylhem Aznar. Distributed under LDP copyright license. If you have questions, please contact Greg Hankins, the Linux HOWTO coordinator, at gregh at sunsite.unc.edu. 1.6. Limited warranty Of course, I disavow any potential liability for the contents of this document. Use of the concepts, examples, and/or other content of this document is entirely at your own risk. 2. Other sources of information 2.1. USENET There is nothing "special" about configuring and running mail software under Linux (any more). Accordingly, you almost certainly do *NOT* want to be posting generic mail-related questions to the comp.os.linux.* newsgroups. Don't post in comp.os.linux hierarchy unless it's really linux specific, for example : "Which options was Debian 1.2 sendmail compiled with ?" or "RedHat 5.0 smail crashes when I run it". Let me repeat that. There is virtually no reason to post anything mail-related in the comp.os.linux hierarchy any more. There are existing newsgroups in the comp.mail.* hierarchy to handle *ALL* your questions. IF YOU POST TO COMP.OS.LINUX.* FOR NON-LINUX-SPECIFIC QUESTIONS, YOU ARE LOOKING IN THE WRONG PLACE FOR HELP. THE MAIL EXPERTS HANG OUT IN THE PLACES INDICATED ABOVE AND GENERALLY DO NOT RUN LINUX. POSTING TO THE LINUX HIERARCHY FOR NON-LINUX-SPECIFIC QUESTIONS WASTES YOUR TIME AND EVERYONE ELSE'S AND IT FREQUENTLY DELAYS YOUR GETTING THE ANSWER TO YOUR QUESTION. GOOD PLACES are : comp.mail.elm the ELM mail system. comp.mail.mh The Rand Message Handling system. comp.mail.mime Multipurpose Internet Mail Extensions. comp.mail.misc General discussions about computer mail. comp.mail.multi-media Multimedia Mail. comp.mail.mush The Mail User's Shell (MUSH). comp.mail.sendmail the BSD sendmail agent. comp.mail.smail the smail mail agent. comp.mail.uucp Mail in the uucp environment. 2.2. Mailing Lists There are many sendmail, smail and qmail mailing lists. You can find addresses in /usr/doc/theoneyouhavechosen. 2.3. Other documents from LDP There is plenty of excellent material provided in the other Linux HOWTO documents and from the Linux DOC project. In particular, you might want to take a look at the following: ╖ on your own computer in /usr/doc/smail or /usr/doc/sendmail :-) ╖ the Linux Networking Administrators' Guide ╖ the Serial Communications HOWTO ╖ the Ethernet HOWTO ╖ the UUCP HOWTO if you're fed via UUCP 2.4. Books The following is a non-inclusive set of books that will help: ╖ "Managing UUCP and USENET" from O'Reilly and Associates is in my opinion the best book out there for figuring out the programs and protocols involved in being a USENET site. ╖ "Unix Communications" from The Waite Group contains a nice description of all the pieces (and more) and how they fit together. ╖ "Sendmail" from O'Reilly and Associates looks to be the definitive reference on sendmail-v8 and sendmail+IDA. It's a "must have" for anybody hoping to make sense out of sendmail without bleeding in the process. ╖ "The Internet Complete Reference" from Osborne is a fine reference book that explains the various services available on Internet and is a great source for information on news, mail and various other Internet resources. ╖ "The Linux Networking Administrators' Guide" from Olaf Kirch of the Linux Documentation Project is available on the net and is also published by (at least) O'Reilly and SSC. It makes a fine one-stop shopping to learn about everything you ever imagined you'd need to know about Unix networking. 3. Requirements 3.1. Hardware There are no specific hardware requirements for mail under Linux. You'll need some sort of 'transport' software to connect to remote systems, which means either TCP/IP or uucp. This could mean that you need a modem or ethernet card, depending on your setup. In most cases, you'll want the fastest modem you can afford, i.e. 57 600 bps currently. In general, you want to have a 16550 UART on your serial board or built into your modem to handle speeds of above 9600 baud. If you don't know what that last sentence means, please consult the comp.dcom.modems group or the various fine modem and serial communications FAQs and periodic postings on USENET. 3.2. Software Well, the problem is here. What shall you do with mail software ? 1) Number of sites Feed more than 100 sites with complicated options for domain name ? Choose sendmail ! Feed less than 100 sites without playing with domain names too much ? Choose smail ! 2) Security Feed more or less than 100 sites but with high security ? Choose qmail ! Feed less than 100 sites but with a standard level of security ? Choose smail ! 3) Different ways to receive mail Feed and being fed by UUCP or FIDO (via ifmail) ? Feed and being fed by POP and internet SMTP ? Choose smail ! Of course, feel free to choose any mail software, informations provided here shall only help you in your choice. Sendmail is perfect for many sites with complicated options, qmail is perfect for high security ; inbetween sendmail and qmail is smail, the best compromise. If you know what you're doing, choose sendmail (and you shouldn't be reading a HOWTO !); otherwise I generally recommand smail. 4. Smail v3.1 Smail3.1 seems to be a de-facto standard transport agent for uucp-only sites and for some smtp sites. It's easy to configure, it compiles without patching from the sources and it's fairly secure. 4.1. Configuring smail Install smail binary from your distribution (I recommand you choose this) or get smail sources and build smail. If you're building smail from sources, you need to have the following in your os/linux file so that 'sed' gives you shell scripts that work properly. CASE_NO_NEWLINES=true Once it's installed, config. files will certainly go in /etc/smail (but your mileage may vary if you use old distributions); let's start editing them ! 4.2. config" file # From smart_path=polux smart_transport=uux # To hostname=danmark domains=linux.eu.org visible_name=danmark.linux.eu.org uucp_name=danmark.linux.eu.org # max_message_size=512k # auth_domains=foo.bar # more_hostnames=barberouge:barberouge.polux.freenix.fr Well, first, who is feeding you ? I'm fed by "polux" via uucp (i.e. uux transport); naturally you need to change this file according to your own situation. For example, you could by fed by "bargw.bar.foobar.com" via "smtp", in that case you don't need a transport file and can define "-transport_file " to indicate you don't need one. You can also use "postmaster_address = yourname", hide the network topology in outgoing addresses (if you're a gateway) using "visible_name", set which aliases address can also be used for the email you receive, using "more_hostnames". See smail documentation for more details or the examples in /usr/doc/smail/examples to see if any match your situation. 4.3. directors" file # aliasinclude - expand ":include:filename" addresses produced by alias files # This entry and the next one are pretty much boiler-plate. Reasons # for making significant changes are few. The sole purpose of these # is to match and expand addresses of the form: # :include:pathname # which may occur in alias files or mailing-list/forward files # (produced by any director with a driver of forwardfile). aliasinclude: driver = aliasinclude, # use this special-case driver nobody; # associate nobody user with addresses # when mild permission violations # are encountered copysecure, # get permissions from alias director copyowners, # get owners from alias director # forwardinclude - expand ":include:filename" addrs produced by forward files forwardinclude: driver = forwardinclude, # use this special-case driver nobody; copysecure, # get perms from forwarding director copyowners, # get owners from forwarding director # aliases - search for alias expansions stored in a database # This is the standard aliases file. It is used for generic things, # like mapping root, postmaster, MAILER-DAEMON and uucp to site # admins, creating some small system alias expansions, and such. In # this site configuration, the aliases file is used mostly for # machine-specific aliasing/forwarding information. Global forwarding # information should be put in the "forward" database. aliases: driver=aliasfile, # general-purpose aliasing director -nobody, # all addresses are associated # with nobody by default, so setting # this is not useful. sender_okay, # don't remove sender from expansions owner=owner-$user; # problems go to an owner address file=/etc/aliases, modemask=002, # should not be globally writable optional, # ignore if file does not exist proto=lsearch, # unsorted ASCII file # forward - search for expansions stored in a forwarding database # This is the subdomain-wide user forwarding database. Entries are # maintained here for current or past users, to forward their mail to # their preferred mail-reading machine. The forward database is # shipped around the TCP/IP network as changes are made, to keep the # network consistent. #forward: # driver = aliasfile, # general-purpose aliasing director # -nobody, # all addresses are associated # # with nobody by default, so setting # # this is not useful. # owner = real-$user; # problems go to an owner address # # file = /etc/forward, # modemask = 002, # proto = dbm, # use dbm(3X) library for access # dotforward - expand .forward files in user home directories # For users that have an entry in the "forward" database, a ".forward" # file is only used if it is on the "home" machine, as identified in # the forward database. If used, it is treated as a list of addresses # to which mail should be delivered, rather than (or in addition to) # the user identified in the local address. dotforward: driver = forwardfile, # general-purpose forwarding director owner = postmaster, nobody, sender_okay; file = ~/.forward, # .forward file in home directories checkowner, # the user can own this file owners = root, # or root can own the file modemask = 002, # it should not be globally writable caution = daemon:root, # don't run things as root or daemon # be extra carefull of remotely accessible home directories unsecure = "~uucp:/tmp:/usr/tmp:/var/tmp" # forwardto - expand a "Forward to " in user mailbox files # This emulates the V6/V7/System-V forwarding mechanism which uses a # line of forward addresses stored at the beginning of user mailbox files # prefixed with the string "Forward to " forwardto: driver = forwardfile, owner = postmaster, nobody, sender_okay; file = /var/spool/mail/${lc:user}, # point at user mailbox files forwardto, # enable "Forward to " function checkowner, # the user can own this file owners = root, # or root can own the file modemask = 0002, # under System V, group mail can write caution = daemon:root # don't run things as root or daemon # user - match users on the local host with delivery to their mailboxes user: driver = user; # driver to match usernames transport = local # local transport goes to mailboxes # real_user - match usernames when prefixed with the string "real-" # This is useful for allowing an address which explicitly delivers to a # user's mailbox file. For example, errors in a .forward file expansion # could be delivered here, or forwarding loops between multiple machines # can be resolved by using a real-username address. Also, users that # wish to use mail as a means of transferring data to a machine that # is not their "home" machine can mail to real-login-name@remote.host. real_user: driver = user; transport = local, prefix = "real-" # for example, match real-root # lists - expand mailing lists stored in a list directory # mailing lists can be created simply by creating a file in the # /etc/smail/lists directory. lists: driver = forwardfile, caution, # flag all addresses with caution nobody, # and then associate the nobody user owner = owner-$user; # system V sites may wish to use # o-$user, as owner-$user may be # too long for a 14-char filename. file = lists/${lc:user} # lists is under $smail_lib_dir # owners - expand mailing lists stored in a list owner directory # mailing lists owner lists can be created simply by creating a file # in the /etc/smail/lists/owner directory. Mailing list owners # are sent locally generated errors dealing with a mailing list of the # same name. To create an owner list for a mailing list, create a # file with the name of the list in /etc/smail/lists/owner. This # will create a list address of owner-listname, as is used by the # "lists" director above. owners: driver = forwardfile, caution, # flag all addresses with caution nobody, # and then associate the nobody user owner = postmaster; # system V sites may wish to use # o-$user, as owner-$user may be # too long for a 14-char filename. prefix = "owner-", file = lists/owner/${lc:user} # lists is under $smail_lib_dir # request - expand mailing lists stored in a list request directory # mailing lists request lists can be created simply by creating a file # in the /etc/smail/lists/request directory. Request addresses # are typically used as a standard address for queries about a mailing # list. For example, requests for additions or deletions to a list # will generally be sent to "list-request", which should be set up to # forward to the appropriate person or persons. request: driver = forwardfile, caution, # flag all addresses with caution nobody, # and then associate the nobody user owner = postmaster; # system V sites may wish to use # o-$user, as owner-$user may be # too long for a 14-char filename. suffix = "-request", file = lists/request/${lc:user} # lists is under $smail_lib_dir You shouldn't need to change anything here, only mailing list options if you intend to run some using smail, or forwards options if, for example, you want to disable forwarding. 4.4. fidopaths" file Create such a file only if you're using ifmail and FIDO. 4.5. routers" file # forces - force certain paths # This database exists as a means of hardcoding the paths to various # machines or domains. It is for use in creating temporary tweaks to # the other routint databases. To change the database, edit the file # maps/force.path and type "make" in the maps/ subdirectory. forces: driver = pathalias, # router to search paths file method = /etc/smail/maps/table; # transports are in this file file = forcepaths, # file containing force path info proto = lsearch, # use the sorted path file optional, reopen # close when not being used uucp_neighbors: driver=uuname, # use a program which returns neighbors transport=uux; cmd="/usr/bin/uuname -a", # specifically, use the uuname program # domain=uucp # strip ending ".uucp" # smart_host - a partically specified smarthost director # If the config file attribute smart_path is defined as a path from the # local host to a remote host, then hostnames not matched otherwise will # be sent off to the stated remote host. The config file attribute # smart_transport can be used to specify a different transport. # If the smart_path attribute is not defined, this router is ignored. smart_host: driver = smarthost, # special-case driver transport = uux # by default deliver over UUCP # path=phreak # ifmail - to send mails to fidonet and vice versa ifmail: driver=pathalias, transport=ifmail; file=fidopaths, proto=lsearch You should only include ifmail chapter if you use ifmail for FIDO mails. Note you can also change transport mode from "uux" (ie UUCP) to, for example, "smtp" or even 'hardcode the paths to various machines or domains' in "/etc/smail/maps/table". 4.6. transports" file # local - deliver mail to local users # Tell smail to append directly to user mailbox files in the /var/spool/mail # directory. #local: driver = appendfile, # append message to a file # -return_path, # include a Return-Path: field # local, # use local forms for delivery # from, # supply a From_ envelope line # unix_from_hack; # insert > before From in body # # file = /var/spool/mail/${lc:user}, # use this location for Linux # # Note, mail spool must be 1777 # file = ~/mailfile, # use this location for better security # group = mail, # group to own file for System V # mode = 0660, # under System V, group mail can access # suffix = "\n", # append an extra newline # append_as_user, # This allows each user to have a ~/.procmailrc file to control filtering # of mail and saving mail from mail lists in separate mailboxes if they wish. local: +inet, -uucp, driver = pipe, # append message to a file return_path, # include a Return-Path: field local, # use local forms for delivery from, # supply a From_ envelope line unix_from_hack; # insert > before From in body cmd = "/usr/bin/procmail", # use procmail for local delivery parent_env, # environment info from parent addr pipe_as_user, # use user-id associated with address umask = 0022, # umask for child process # -ignore_status, # exit status should be believed # -ignore_write_errors, # retry on broken pipes # pipe - deliver mail to shell commands # This is used implicitly when smail encounters addresses which begin with # a vertical bar character, such as "|/usr/lib/news/recnews talk.bizarre". # The vertical bar is removed from the address before being given to the # transport. #pipe: driver = pipe, # pipe message to another program # return_path, local, from, unix_from_hack; # # cmd = "/bin/sh -c $user", # send address to the Bourne Shell # parent_env, # environment info from parent addr # pipe_as_user, # use user-id associated with address # umask = 0022, # umask for child process # -log_output, # do not log stdout/stderr # ignore_status, # exit status may be bogus, ignore it # ignore_write_errors, # ignore broken pipes # file - deliver mail to files # This is used implicitly when smail encounters addresses which begin with # a slash or squiggle character, such as "/usr/info/list_messages" or # perhaps "~/Mail/inbox". #file: driver = appendfile, # return_path, local, from, unix_from_hack; # # file = $user, # file is taken from address # append_as_user, # use user-id associated with address # expand_user, # expand ~ and $ within address # check_path, # suffix = "\n", # mode = 0644 # uux - deliver to the rmail program on a remote UUCP site # # As many as five recipient addresses will be delivered to the remote # host in one UUCP transaction. uux: driver = pipe, -uucp, inet, # uucp, # use UUCP-style addressing forms from, # supply a From_ envelope line max_addrs = 5, # at most 5 addresses per invocation max_chars = 200; # at most 200 chars of addresses # the -r flag prevents immediate delivery, parentheses around the # $user variable prevent special interpretation by uux. cmd = "/usr/bin/uux - -r -g$grade $host!rmail $((${strip:user})$)", # cmd="/usr/bin/uux - $host!rmail $(($user)$)", ignore_write_errors, # ignore broken pipes umask = 0022, # pipe_as_sender, # uux_one_addr - deliver mail over UUCP to a remote host that can take # one address at a time. # This is often necessary when delivering to a site running an unmodified # version of 4.1BSD. uux_one_addr: driver = pipe, uucp, # use UUCP-style addressing forms from; # supply a From_ envelope line # the -r flag prevents immediate delivery cmd = "/usr/bin/uux - -r -g$grade $host!rmail (${strip:user})", umask = 0022, pipe_as_sender queueonly: driver = pipe; # send the message to a pipe cmd = "/usr/lib/sendmail -Q -f $sender -bm $user", # use getmail for local delivery user=root, # execute getmail as "root" group=mail, # execute getmail as "mail" parent_env, # environment info from parent addr -pipe_as_user, # use user-id associated with address umask = 0007, # umask for child process # to deliver the message. The smtp transport is included only if BSD # networking exists. # The uucp attribute can be specified for transfers within the UUCP # zone. The inet attribute must be specified for transfers within the # Internet. # NOTE: This is hardly optimal, a backend should exist which can handle # multiple messages per connection. # ALSO: It may be necessary to restrict max_addrs to 100, as this is the # lower limit SMTP requires an implementation to handle for one # message. smtp: driver=tcpsmtp, inet, # if UUCP_ZONE is not defined # uucp, # if UUCP_ZONE is defined -max_addrs, -max_chars; # no limit on number of addresses short_timeout=5m, # timeout for short operations long_timeout=2h, # timeout for longer SMTP operations service=smtp, # connect to this service port # For internet use: uncomment the below 4 lines use_bind, # resolve MX and multiple A records defnames, # use standard domain searching defer_no_connect, # try again if the nameserver is down local_mx_okay, # fail an MX to the local host ifmail: from,received,max_addrs=5,max_chars=200, driver=pipe; pipe_as_sender, cmd="/usr/local/bin/ifmail -x9 -r$host $((${strip:user})$)" You should include an ifmail chapter only if you use ifmail for FIDO mails. Apart from that, you shouldn't need to edit anything in this file which defines transport agents (like uux, smtp ...) you can use as parameters in other config. files. Note I commented out some parts, like "pipes" or "file", to enhance security. 4.7. maps/" directory It contains map and table files : First, map file #N foo.bar foo2.bar2 #S AT 486/RedHat Linux 1.2.13 #O organization #C contact #E administration (email) #T phone #P address #R #U hosts connected via uucp #W created/edited by # hname polux hname linux.eu.org hname = polux hname = polux.linux.eu.org Once again, edit this file to match you situation (I'm fed by polux.linux.eu.org). Now table file * uux You can define different transports to different path, for exemple "smtp" for the machines in your local network, "uux" (i.e. uucp) for the rest of the world or vice-versa (I'm using uucp for any outgoing mail, therefore I use "*" !). 4.8. Other good examples The previous files are the one I currently use for my site, you shouldn't encounter any problem using them as samples/basis for your own files. The following files are provided only as good exemples to configure smail a different way. #ident "@(#) transports,v 1.2 1990/10/24 05:20:46 tron Exp" # See smail(5) for a complete description of the contents of this file. # local - deliver mail to local users # # Tell smail to append directly to user mailbox files in the /usr/mail # directory. local: driver = appendfile, # append message to a file return_path, # include a Return-Path: field local, # use local forms for delivery from, # supply a From_ envelope line unix_from_hack; # insert > before From in body file = /usr/mail/${lc:user}, # use this location for System V group = mail, # group to own file for System V mode = 0660, # under System V, group mail can access suffix = "\n", # append an extra newline append_as_user, # pipe - deliver mail to shell commands # # This is used implicitly when smail encounters addresses which begin with # a vertical bar character, such as "|/usr/lib/news/recnews talk.bizarre". # The vertical bar is removed from the address before being given to the # transport. pipe: driver = pipe, # pipe message to another program return_path, local, from, unix_from_hack; cmd = "/bin/sh -c $user", # send address to the Bourne Shell parent_env, # environment info from parent addr pipe_as_user, # use user-id associated with address umask = 0022, # umask for child process -log_output, # do not log stdout/stderr ignore_status, # exit status may be bogus, ignore it ignore_write_errors, # ignore broken pipes # file - deliver mail to files # # This is used implicitly when smail encounters addresses which begin with a # slash or squiggle character, such as "/usr/info/list_messages" or perhaps # "~/Mail/inbox". file: driver = appendfile, return_path, local, from, unix_from_hack; file = $user, # file is taken from address append_as_user, # use user-id associated with address expand_user, # expand ~ and $ within address suffix = "\n", mode = 0644 # uux - deliver to the rmail program on a remote UUCP site # # As many as five recipient addresses will be delivered to the remote host in # one UUCP transaction. uux: driver = pipe, uucp, # use UUCP-style addressing forms from, # supply a From_ envelope line max_addrs = 5, # at most 5 addresses per invocation max_chars = 200; # at most 200 chars of addresses # the -r flag prevents immediate delivery, parentheses around the # $user variable prevent special interpretation by uux. cmd = "/usr/bin/uux - -r -g$grade $host!rmail $((${strip:user})$)", umask = 0022, pipe_as_sender # uux_one_addr - deliver mail over UUCP to a remote host that can take one # address at a time. # # This is often necessary when delivering to a site running an unmodified # version of 4.1BSD. uux_one_addr: driver = pipe, uucp, # use UUCP-style addressing forms from; # supply a From_ envelope line # the -r flag prevents immediate delivery cmd = "/usr/bin/uux - -r -g$grade $host!rmail (${strip:user})", umask = 0022, pipe_as_sender # demand - deliver to a remote rmail program, polling on demand demand: driver = pipe, uucp, from, max_addrs = 5, max_chars = 200; # with no -r flag, try to contact remote site immediately cmd = "/usr/bin/uux - -g$grade $host!rmail $(($user)$)", umask = 0022, pipe_as_sender # uusmtp - deliver to the rsmtp program on a remote UUCP site # # Deliver using a simple Batched SMTP protocol to the remote machine. # This allows much more arbitrary addresses to be used. It also # removes the limit on recipient addresses per invocation of uux. uusmtp: driver = pipe, bsmtp, # send batched SMTP commands -max_addrs, # there is no limit on the number or -max_chars; # total size of recipient addresses. # supply -r to prevent immedate delivery, the recipient addresses # are stored in the data sent to the standard input of rsmtp. cmd = "/usr/bin/uux - -r -g$grade $host!rsmtp", umask = 0022, pipe_as_sender # demand_uusmtp - deliver to a remote rsmtp program, polling on demand demand_uusmtp: driver = pipe, bsmtp, -max_addrs, -max_chars; # with no -r flag, try to contact remote site immediately cmd = "/usr/bin/uux - -g$grade $host!rsmtp", umask = 0022, pipe_as_sender # smtp - deliver using SMTP over TCP/IP # # Connect to a remote host using TCP/IP and initiate an SMTP conversation to # deliver the message. The smtp transport is included only if BSD networking # exists. # NOTE: It may be necessary to restrict max_addrs to 100, as this is the # lower limit SMTP requires an implementation to handle for one # message. smtp: driver = smtp, -max_addrs, -max_chars #ident "@(#) table,v 1.2 1990/10/24 05:20:31 tron Exp" # This file names the transports that are to be used in delivering # to specific hosts from bargw. #host transport #-------- --------- curdsgw demand_uusmtp # deliver using batched SMTP oldbsd uux_one_addr # 4.1BSD sites cannot take more than one addr sun demand # call sun when their is mail to send * uux # for all others, poll at intervals 4.9. Restarting inetd To run smail as a smtp daemon, add one of the following to /etc/inetd.conf: smtp stream tcp nowait root /usr/bin/smtpd smtpd or: smtp stream tcp nowait root /usr/sbin/tcpd /usr/sbin/in.smtpd Outgoing mail gets sent automatically, when using elm. 4.10. Smail with smtp Generally, ISPs use smtp, therefore you shouldn't have any problems sending your mail. If your internet link is down when you send mail, then the mail sits in "/var/spool/smail/input". When the link next comes up, "runq" is run which causes the mail to be sent. However, receiving mail is the problem since your provider has many clients to look after, not only you ! Usually, you can retreive your mail via the POP protocol, see POP section below. 5. Sendmail+IDA For big sites, sendmail is worth choosing, due to the incredible ease of use, but you must decide which you want between sendmail+IDA and sendmail 8.x : ╖ If you use an old kernel (1.0) : sendmail+IDA ╖ If you use a not so old kernel (1.2) : sendmail+IDA and source code editing ╖ Recent kernel (2.0) will choose sendmail 8.x Remember, linux newbies or people concerned by security / ease of configuration should rather try using smail or qmail, which are easier to use and safer. 5.1. Source installation ╖ cd / ; tar -zxvf sendmail5.67b+IDA1.5.tpz ╖ cd to /usr/local/lib/mail/CF and copy the sample.m4 local.m4 file to "yourhostname.m4". Edit out the distributed hostname, aliases, smarthost and put in the correct one for your site. The default file is for a uucp-only site who has domainized headers and who talks to a smart host. Then "make yourhostname.cf" and move the resulting file to /etc/sendmail.cf ╖ if you are uucp-only, you do *NOT* need to create any of the tables mentioned in the README.linux file. You'll just have to touch the files so that the Makefile works. Just edit the .m4 file, make sendmail.cf and start testing it. ╖ if you're uucp-only and you talk to sites in addition to your "smart-host", you'll need to add uucpxtable entries for each (or mail to them will also go through the smart host) and run dbm against the revised uucpxtable. ╖ If you run Rich Braun's original binary distribution of 5.67a, you'll need to freeze the configuration if you change your .cf file with "/usr/lib/sendmail -bz" to make the changes take effect. You should also update your version to at least 5.67b since there is a nasty security hole in 5.67a and earlier. Another nice thing is that if you have mail.debug set and you run syslogd, your incoming and outgoing mail messages will get logged. See the "/etc/syslog.conf" file for details. The sources for sendmail+IDA can be found at vixen.cso.uiuc.edu ; they require no patching to run under Linux if you're running something like a kernel of 1.00. If you're running a kernel > 1.1.50, you get the fun of reversing most of the Linux-specific patches that are now in the vanilla sources. (I *did* told you this sendmail was only for old kernels :-) It's extremely obvious where this needs to be done : just type "make" and when it blows up, go to that line in the sources and comment out the Linux-specific code that's in there. If you're going to run sendmail+IDA, I strongly recommend you go to the sendmail5.67b+IDA1.5 version since all required Linux-specific patches are now in the vanilla sources and several security holes have been plugged that WERE (!!!) in the older version you may have grabbed or built before about December 1st, 1993. Now linux kernel is 2.0, you should use sendmail 8.x insted of sendmail+IDA, but I told you'd better choose sendmail 8.x :-) 5.2. The sendmail.m4 file Sendmail+IDA requires you to set up a sendmail.m4 file rather than editing the sendmail.cffile directly. The nice thing about this is that it is simple to set up mail configurations that are extremely difficult (if not totally impossible for most people to set up correctly) in smail or traditional sendmail. The sendmail.m4 file that corresponds to the above smail example looks like the following: dnl #------------------ SAMPLE SENDMAIL.M4 FILE ------------------ dnl # dnl # (the string 'dnl' is the m4 equivalent of commenting out a line) dnl # dnl # you generally don't want to override LIBDIR from the compiled in paths dnl #define(LIBDIR,/usr/local/lib/mail)dnl # where all support files go define(LOCAL_MAILER_DEF, mailers.linux)dnl # mailer for local delivery define(POSTMASTERBOUNCE)dnl # postmaster gets bounces define(PSEUDODOMAINS, BITNET UUCP)dnl # don't try DNS on these dnl # dnl #------------------------------------------------------------- dnl # dnl # names we're known by define(PSEUDONYMS, myhostname.subdomain.domain myhostname.UUCP) dnl # dnl # our primary name define(HOSTNAME, myhostname.subdomain.domain) dnl # dnl # our uucp name define(UUCPNAME, myhostname)dnl dnl # dnl #------------------------------------------------------------- dnl # define(UUCPNODES, |uuname|sort|uniq)dnl # our uucp neighbors define(BANGIMPLIESUUCP)dnl # make certain that uucp define(BANGONLYUUCP)dnl # mail is treated correctly define(RELAY_HOST, my_uucp_neighbor)dnl # our smart relay host define(RELAY_MAILER, UUCP-A)dnl # we reach moria via uucp dnl # dnl #-------------------------------------------------------------------- dnl # dnl # the various dbm lookup tables dnl # define(ALIASES, LIBDIR/aliases)dnl # system aliases define(DOMAINTABLE, LIBDIR/domaintable)dnl # domainize hosts define(PATHTABLE, LIBDIR/pathtable)dnl # paths database define(GENERICFROM, LIBDIR/generics)dnl # generic from addresses define(MAILERTABLE, LIBDIR/mailertable)dnl # mailers per host or domain define(UUCPXTABLE, LIBDIR/uucpxtable)dnl # paths to hosts we feed define(UUCPRELAYS, LIBDIR/uucprelays)dnl # short-circuit paths dnl # dnl #-------------------------------------------------------------------- dnl # dnl # include the 'real' code that makes it all work dnl # (provided with the source code) dnl # include(Sendmail.mc)dnl # REQUIRED ENTRY !!! dnl # dnl #------------ END OF SAMPLE SENDMAIL.M4 FILE ------- 5.3. Defining a local mailer Unlike most Unix distributions, Linux does not come with a local mail delivery agent by default. Now, deliver or procmail is generally installed, so no complexity will be added to this already very complex setup. I recommend using the commonly available deliver or procmail programs, which can be optional packages in a some Linux distributions. In order to do so, you need to define a LOCAL_MAILER_DEF in the sendmail.m4 file that points to a file that looks like: # -- /usr/local/lib/mail/mailers.linux -- # (local mailers for use on Linux ) Mlocal, P=/usr/bin/deliver, F=SlsmFDMP, S=10, R=25/10, A=deliver $u Mprog, P=/bin/sh, F=lsDFMeuP, S=10, R=10, A=sh -c $u There is a also built-in default for deliver in the Sendmail.mc file that gets included into the sendmail.cf file. To specify it, you would not use the mailers.linux file but would instead define the following in your sendmail.m4 file: dnl --- (in sendmail.m4) --- define(LOCAL_MAILER_DEF, DELIVER)dnl # mailer for local delivery Unfortunately, Sendmail.mc assumes deliver is installed in /bin, which is not the case with Slackware1.1.1 (which installs it in /usr/bin). In that case you'd need to either fake it with a link or rebuild deliver from sources so that it resides in /bin. Please note procmail is generally better than deliver, for example for mail filtering. 5.4. The sendmail+IDA dbm tables Setting up special behavior for sites or domains is done through a number of optional dbm tables rather than editing the sendmail.cf file directly. Refer to the July-1994 issue of Linux Journal (if you can still find it :-), to the docs in the sources, or to the sendmail chapter in the newest version of the Linux DOC Project Networking Administration Guide which will be available real-soon-now for more details. ╖ mailertable - defines special behavior for remote hosts or domains. ╖ uucpxtable - forces UUCP delivery of mail to hosts that are in DNS format. ╖ pathtable - defines UUCP bang-paths to remote hosts or domains. ╖ uucprelays - short-circuits the pathalias path to well-known remote hosts. ╖ genericfrom - converts internal addresses into generic ones visible to the outside world. ╖ xaliases - converts generic addresses to/from valid internal ones. ╖ decnetxtable - converts RFC-822 addresses to DECnet-style addresses. 5.5. So which entries are really required? When not using any of the optional dbm tables, sendmail delivers mail via the RELAY_HOST and RELAY_MAILER) defined in the sendmail.m4 file used to generate sendmail.cf. It is easily possible to override this behavior through entries in the domaintable or uucpxtable. A generic site that is on Internet and speaks Domain Name Service, or one that is UUCP-only and forwards all mail via UUCP through a smart RELAY_HOST, probably does not need any specific table entries at all. Virtually all systems should set the DEFAULT_HOST and PSEUDONYMS macros, which define the canonical site name and aliases it is known by. If all you have is a relay host and relay mailer, you don't need to set these defaults since it works automagically. UUCP hosts will probably also need to set UUCPNAME to their official UUCP name. They will also probably set RELAY_MAILER and RELAY_HOST which enable smart-host routing through a mail relay. The mail transport to be used is defined in RELAY_MAILER and should usually be UUCP-A for UUCP sites. If your site is SMTP-only and talks `Domain Name Service', you would change the RELAY_MAILER. If you're a SLIP site, you might want to take the easy way out and just forward all outgoing mail to your service provider to do the right thing with. To do so, you'd want to define ISOLATED_DOMAINS and VALIDATION_DOMAINS to be your domain, you'd also want to define RELAY_HOST to be your service provider and RELAY_MAILER to be TCP. Of course, you want to ask permission before you set any system up as your general purpose relay. 5.6. Sendmail 8.x Sendmail 8.7.x from Berkeley was the latest major revision after sendmail5. It had wonderful built-in support for building under Linux : just "make linux" and all was set. You'll probably be best served by grabbing one of the various binary distributions off of the usual Linux archive sites rather than fighting things like Berkeley dbm yourself. There's a nice distribution of sendmail 8.6.12 from Jason Haar - j.haar at lazerjem.demon.co.uk on sunsite.unc.edu in /pub/Linux/system/Mail/delivery/sendmail-8.6.12-bin.tgz that has the source documentation and a very nice quickie description of how to run sendmail v8 for common configurations. The bottom line with sendmail v8 is that you want to configure the bare minimum necessary to get the job done ; the following is an example that should get you close at least. 5.7. A sample 8.7.x mc file Much like sendmail+IDA, sendmail v8 uses m4 to process a config file into a full sendmail.cf that sendmail uses. The following is my current mc file for my site (ppp to Internet for outgoing mail, uucp for incoming mail). dnl divert(-1) #--------------------------------------------------------------------- # # this is the .mc file for a linux host that's set up as follows: # # - connected to Internet for outbound mail (ppp here) # - connected via UUCP for incoming mail # - domainized headers # - no local mailer (use 'deliver' instead) # - no DNS running so don't canonicalize outgoing via DNS # - all non-local outbound mail goes to the RELAY_HOST over smtp # (we run ppp and let our service provider do the work) # # vds 3/31/95 # #--------------------------------------------------------------------- include(`../m4/cf.m4') VERSIONID(`linux nodns relays to slip service provider smarthost')dnl Cwmyhostname.myprimary.domain myhostname.UUCP localhost OSTYPE(linux) FEATURE(nodns)dnl FEATURE(always_add_domain)dnl FEATURE(redirect) FEATURE(nocanonify) dnl MAILER(local)dnl MAILER(smtp)dnl MAILER(uucp)dnl define(`RELAY_HOST', smtp:my.relay.host.domain) define(`SMART_HOST', smtp:my.relay.host.domain) define(`UUCP_RELAY', smtp:my.relay.host.domain) define(`LOCAL_MAILER_PATH', `/bin/deliver') define(`LOCAL_MAILER_ARGS', `deliver $u') 5.8. Sendmail v8 tidbits There are a few differences I suppose to the 'IDA bigots' among us. So far, I've found the following: Instead of 'runq', you type 'sendmail -q' to run the queue ! 5.9. Local Delivery Agents Unlike most operating systems, Linux did not have mail "built-in" : you needed a program to deliver the local mail, like "lmail", "procmail" or "deliver". However, every recent distribution includes a local mailer ! Documentation for how to use either for local delivery is in the sendmail5.67b+IDA1.5 binary release (on sunsite) mentioned above. 6. POP mail This section also concerns IMAP, not very different from POP. 6.1. History On a workstation network, mail has always been a problem: ╖ Either you use "user@computer.foo.com" with problems when "computer" is down, make your network known to the people outside, have different addresses for a same person switching to another computer, ... ╖ Either you take a mail hub, "mailhost.foo.com" with rules for rewriting, so every user seems to post from the same address, even if they are on different computers. But in that case, how can user read their mail ? Using a rsh with elm ? :-) It would overload our mail hub ! One method was forwarding or UUCP, smtp, etc. but it's too complicated. Then came POP/IMAP, both with security problems at the beginning, now fixed using ssh on new versions) : a mail program has sometimes to be set locally (like sendmail, smail, qmail if, for example, you use elm, but mozilla will avoid that !) however, getting and sending Email is simpler. 6.2. Getting mail Here come POP's main drawbacks : the password is sent as a clear text on the network, and some mail readers just don't know POP : you must choose a POP-aware mailer, like Pine, Emacs, Netscape, Mutt ... Password problem can be solved creating a crypted "channel" to have POP on it or using APOP or RPOP extensions. The mail reader problem can be solved either by changing mail reader (mozilla is POP ready, as are Emacs and pine) or by using a POP "mail sucker" with a local mail program. gwpop (a Good Way to POP) is worth using since it creates a crypted "channel" and puts mail directly in the "spool". However, it depends on Perl ... I can also recommand fetchmail, which is actively supported. Otherwise you can use one of the various pop clients available for linux, for exaple if your login is john and your password PrettySecret, you will run : $ popclient -3 -v mail.acme.net -u john -p "PrettySecret" -k -o JOHN-INET-MAIL (see popclient manpage for the exact meanings of the above options !) 6.3. Sending mail For this, you must use smtp-aware mail software, like qmail, sendmail, smail or mozilla (this one does everything : mail reader, POP receive, smtp send !) Go to one of the previous sections to install and configure the one you like best. Then, will you will reach "Testing", try to send some mail to a local account on the mail hub. 6.4. Reading mail If your program doesn't do everything itself, you can install elm, pgp, mush, pine ... many good programs are freely available for linux platforms ! 6.5. Testing To check your mail server has pop, try : $ telnet mailhost 110 If it works, you will get something like "OK Pop server (...) starting" : type "quit" ! To install a ssh crypted "channel", first test your mail server typing : $ ssh mailhost date If you get the date, you should be OK. Please note ssh will not ask for a password, therefore you must create a ".shosts" file on the mail server, containing client's name. To test ssh port redirection (which gwpop uses), type : $ ssh -n -f -L 12314:localhost:110 mailhost sleep 30 then $ telnet localhost 12314 Then will you hopefully see mail hub's pop banner. If you don't use ssh, don't forget to comment out $ssh on gwpop script. To check whether procmail is running, try "procmail -v" 6.6. Using Now you can edit gwpop Perl script to check everything is ok, then run gwpop : $ gwpop -v your-username POP password on mailhost: yoursecretpasword If gwpop "error messages" are normal, the mail from mail hub will be downloaded to your local machine whereever you told gwpop to put it. (please test with some mail !). You can also use gwpop as a daemon : $ gwpop -d $HOME/tmp your-username gwpop messages are then sent to syslog and gwpop will run endlessly ; a "HUP" signal will force gwpop to get your mail. You can get POP software here used on : ftp://ftp.pasteur.fr/pub/Network/gwpop ftp://ftp.informatik.rwth-aachen.de/pub/packages/procmail http://www.cs.hut.fi/ssh/ 7. Mail "user agents" This section contains information related to "user agents", which means the software the user sees and uses. This software relies on the "transport agents" mentioned above. Many other mail "User Agents" are available now (pine, mush ...) but I haven't found any linux-specific information to tell on them. Please tell me if I'm missing something ! 7.1. Elm Elm compiles, installs and runs flawlessly under Linux. For more information, see the elm sources and installation instructions. Elm and filter need to be mode 2755 (group mail) with /var/spool/mail mode 775 and group mail. If you use a binary distribution, you'll need to create a "/usr/local/lib/elm/elm.rc" file to override the compiled-in hostname and domain information: ╖ replace "subdomain.domain" with your domain name replace ╖ "myhostname" with you un-domainized hostname replace #---------- /usr/local/lib/elm/elm.rc ------------------ # # this is the unqualified hostname hostname = myhostname # # this is the local domain hostdomain = subdomain.domain # # this is the fully qualified hostname hostfullname = myhostname.subdomain.domain # #-------------------------------------------------------- One thing you want to be aware of is that if you have Elm compiled to be MIME enabled, you need metamail installed and in your path or Elm will not be able to read MIME mail you've received. Metamail is available on thumper.bellcore.com and of course via "archie". In the "too cool to be true" category, there is a distribution of Elm-2.4.24 that is "PGP-aware". To try it, grab the file ftp://ftp.viewlogic.com/pub/elm-2.4pl24pgp3.tar.gz, which is elm2.4.24 with PGP hooks added. You configure and build it the same way you do normal Elm, which means you probably need to add the patches mentioned above. For what it's worth, I run it here and like it a lot. Of course, there must be more recent versions available, including elm- ME+. While this item is not Linux-specific, it's perceived (wrongly) to be a nagging Elm bug nevertheless. We've heard that Elm sometimes fails with a message that it's unable to malloc() some massive number of bytes. The identified workaround is to remove the post-processed global mail aliases (aliases.dir and aliases.pag). THIS IS NOT A BUG IN ELM, it's an error in configuration of Elm by whomever you got your binary distribution of Elm from. Elm has an enhanced and non-compatible, format for aliases ; you need to ensure that the path Elm uses for aliases is different from the path sendmail/smail uses. From the volume of reports of this problem, it's apparent that at least one major distribution 'on the street' has in the past been misconfigured. (from scot at catzen.gun.de (Scot W. Stevenson) ) The current metamail package requires csh for some of its scripts. Failure to have csh (or tcsh) will cause most interesting errors... 7.2. Mailx Save yourself the pain : just go and grab the mailx kit from Slackware 2.1.0 or later, which has a nice implementation of mailx5.5. If you're into building from sources, mailx v5.5 compiles without patching under Linux if you have "pmake" installed. If anybody is still using it, I strongly recommend removing the old "edmail" stuff from SLS1.00 and replacing it with mailx. 7.3. Other user agents The following also are known to run under Linux. Consult "archie" for details regarding how to find them... ╖ Pine - from the Univ. of Washington ╖ Metamail - allows MIME support ╖ mh - yet another way to handle mail ╖ deliver - file/process mail based on rules ╖ procmail - file/process mail based on rules ╖ Majordomo - manages e-mail lists ╖ Mserv - provide files-by-mail 8. Acknowledgements The following people have helped in the assembly of the information and experience that helped make this document possible: Steve Robbins, Ian Kluft, Rich Braun, Ian Jackson, Syd Weinstein, Ralf Sauther, Martin White, Matt Welsh, Ralph Sims, Phil Hughes, Scot Stevenson, Neil Parker, Stephane Bortzmayer and especially many thanks to Vince Shankan for his huge contribution. If I forgot anybody, my apologies : just Email me !