Standards used for Internet e-mail have remained fairly static for a number of years. However, the recent development of new standards, and their widespread adoption in both client and server software, makes the issues in selecting an e-mail server different to what they were even twelve months ago. Let us look at some of the main features an e-mail server might have.
SMTP (Simple Mail Transfer Protocol) is a much forgotten but vital standard in Internet e-mail. This is the protocol used by servers to talk to each other, and by the client software to send e-mail. It should be incorporated into every e-mail server. It is worth mentioning because if you offer services such as broadcast e-mailing, running an SMTP server on a separate machine will reduce the strain on your main e-mail server.
POP stands for "Post Office Protocol" and is currently the most popular e-mail client protocol. POP3 is a very simple protocol that concerns itself with copying mail from a server to a client computer. You may come across terms such as POP, POP2 and POP3. The main one you should be concerned about is POP3, as the others have fallen into disuse. Most e-mail servers and clients support the extensions to POP3 such as EXTD and AUTH but rarely mention this fact explicitly.
IMAP4 (Internet Mail Access Protocol) is being heralded as the future of Internet e-mail. This is likely to be true due to its inclusion in the latest version of Netscape. IMAP4 is different to POP3 and provides a more flexible e-mail solution. It has enhanced functionality for remote users and is better suited than POP3 for LAN e-mail. All the IMAP4 servers I have seen include support for POP mail.
You should not forget the increasingly rare but highly flexible telnet access to e-mail (buy a cup of coffee in a Net café anywhere in the world, and simply telnet in and read your e-mail). This is one good reason to stick with Linux or some other Unix variant, as telnet access is automatic with Unix systems.
Not an e-mail standard but something you should be aware of is LDAP (Lightweight Directory Access Protocol) which is a standard for Internet Directory Services. Many client packages and e-mail servers now include support for LDAP.
With the number of packages available on the market it is not possible to provide a comprehensive review. For Windows NT, the package I have been impressed with is the Netscape Messaging Server, which is suitable for installations with less that 5000 users. If you are using other Netscape server products, you benefit from consistent management. Several Unix versions (but not Linux) are available.
- Roy Chambers