You should read this section only if your SMTP module is set to receive
messages via TCP/IP.
The Internet is flooded with soliciting E-mail messages distributed to
millions of E-mail addresses. These messages are known as "spam".
Spammers fill your user mailboxes with a huge amount of unwanted messages,
not only overloading the Internet and your Server resources, but making
mail retrieval very slow and difficult for your users.
In order to distribute their messages to thousands and even millions
E-mail addresses, spammers try to use any SMTP mail server on the internet
as a relay: they deliver one copy of the message to each mail server requesting
that it routes the message to 100 addresses. This practice not only overloads
your Server resources, but it places you at risk to be recognized as a spammer
(since messages come from your server).
If your SMTP module can accept incoming TCP connections, your server
can be used by spammers as a mail relay engine: they can distribute their
messages all over the world using your server. They can also send a lot
of soliciting messages to your clients. To protect your site from the known
spammer sites, you can put the IP addresses of the offending hosts into
the SMTP Black List.
When a host with an address included into the Black List connects to
your server and tries to submit a message, it gets an error message from
your SMTP module and mail from that host is not accepted.
To enter data into the Black List, open the SMTP Service Settings dialog
box and click the Black Listed button. A dialog box appears and allows
you to enter the IP addresses of the offending hosts:
 (Disk 2).dmg/Shareware World/Comms & Internet/CommuniGate-SMTP-291/Documentation/SMTP/BlackList.gif/BlackList.gif)
- Each line can contain either one address in the form:
- 12.34.56.78
- or a range of addresses in the form:
- 12.34.50.01-12.34.59.99
There are several Web sites on the Internet that maintain the lists
of known spammers. A special section
on the Stalker Software Web site lists the addresses of the hosts that
abused the mail servers at Stalker Software, Inc. and its subsidiaries.
If your SMTP module can accept incoming TCP connections, your server
can be used by spammers as a mail relay engine: they can distribute their
messages all over the world using your server. To protect your site from
spammers, the system can restrict its relaying functionality.
If all your users employ the CommuniGator application, or other AppleTalk-based
mailers, simply select the Do not Serve Strangers option.
If you have POP and/or IMAP users, put the IP addresses they connect
from into the Own Users dialog box (see the Restrictions
section) and select the Do Not Serve Strangers option.
If your Server acts as a back-up mail server for other hosts, or if
your Server is used as a forwarding ("foreign") mail server for
dial-up some client hosts, open the SMTP Service Settings and click the
Client Hosts button. A dialog box appears and allows you to enter the IP
addresses of these client systems.
Note: your should not repeat the addresses entered in the Our
Users box: mail from those addresses can always be relayed.
If you have dial-up or LAN users that use POP and IMAP mailers and you
do not want the server to consider them "Own Users", enter the
range of the IP addresses they use into the Clients Host dialog box, not
into the Our Users dialog box.
 (Disk 2).dmg/Shareware World/Comms & Internet/CommuniGate-SMTP-291/Documentation/SMTP/ClientHosts.gif/ClientHosts.gif)
Now, when a message is received with the SMTP module via TCP/IP, and
the sender IP address is not found neither in the Client Hosts nor in the
Own Users list, the message is marked as being received "from a stranger".
If this message should be relayed by your server to some other host on
the Internet, and that host is not listed in the Client Hosts list either,
the message is rejected.
As a result, servers and workstations included into the Client Hosts
list can use your server to send (relay) messages to anybody on the Internet,
and any message from the Internet can be relayed to any listed address.
But any message coming from an unlisted system and directed to some other
unlisted system will be rejected. This will prohibit spammers from using
your server as a mail relay.
Since this functionality can affect your legitimate users if you do
not specify their IP addresses correctly, the Do not Serve Strangers option
is available in the SMTP Service Settings. The "stranger-to-stranger" messages are rejected only if this option is selected.