You can use the AppleShare IP mail server on a single computer or on multiple computers.

Single-server mail service

In single-server mail service, when a user sends messages, the mail server stores them until the recipients download the messages to their computers. Everyone using mail service connects to the same server, and the Users & Groups data is stored in one file.

Multiple-server mail service

If your organization has more users or messages than the mail server can handle (the exact number depends on the amount of RAM available to the server, and whether you are using POP or IMAP), you can distribute your mail services across multiple computers.

IMPORTANT: Your software license agreement allows you to run one copy of the mail server on one computer. If you want to install the mail server on more than one computer, you need to purchase additional copies of the software.

There are two ways to share mail servers: store-and-forward and mail relay.

Store-and-forward:
With store-and-forward sharing, each computer running the mail server stores messages addressed to the users who connect to it, and forwards messages addressed to users who connect to other servers. Thus, store-and-forward works by changing the receiving address on the message.

In the following example, both Shasta and Rainier are running the mail server. Shasta is the primary system and Rainier is secondary. Clara connects to the mail server on Shasta to receive mail. Arthur connects to the mail server on Rainier.

Shasta.com Primary system		Rainier.com Secondary system
Clara Account location: shasta.com		Arthur Account location: rainier.com

If Domain Name Service (DNS) is set up on the network, Clara can address mail to Arthur by typing "arthur@rainier.com". Or, because Shasta and Rainier share a Users & Groups file, she can simply type "arthur."

When Clara sends mail to Arthur, her mail application connects to Shasta. Shasta looks up Arthur in its Users & Groups file and sees that his mail is to be forwarded to Rainier. Shasta then opens a connection to Rainier and sends the message. Rainier receives the message, determines that it is addressed to Arthur, and stores the message. The next time Arthur connects to Rainier, his mail application retrieves the message.

Mail relay:
With mail relay, you can send mail via a specific server when the addressee is not local or when you need to use specific capabilities of another server (for example, its ISDN connection to the Internet).

With mail relay, how the server treats a message depends on whether the recipient is local or remote:

•	Local user (in the Users & Groups Data File): The server stores the message until the user's mail application retrieves it.
•	Remote user: The server sends the message to the relay server. The relay server sends it to the user's server, which stores it until the user's mail application retrieves it.

Mail relay does not change the recipient of the message. It uses the specific server as a path for sending the message.

Related topic

Domain Name System (DNS)