Linux Gazette: An Overview of Linux Mail SoftwareAug 05, 2000, 18:13 (0 Talkback[s])
(Other stories by Jim Dennis)
"There are many packages that can supply standard mail services under Linux. Basically the UNIX/Linux e-mail model involves MTA (mail transport agents), MSA (mail storage/access agents) and MUAs (mail user agents). There are also a variety of utilities that don't really quite fit in any of these categories."
"Under Linux there are several MTAs including sendmail, the most common across most forms of UNIX; and D.J. Bernstein's qmail and Wietse Venema's Postfix. These accept and relay mail. This sounds quite simple, but in practice it can be quite complex. There are a number of routing and masquerading options that can be set by administrative policy --- and these amount to programming languages that filter and modify the headers of each message as it is relayed. In addition the process of routing mail and finding user mail boxes (mail stores) can involve arbitrarily complex interactions with various directory services (DNS, passwd files, NIS, LDAP alias/dbm files, and all manner of custom databases)."
"These days MTAs also have to implement anti-spam features that amount to access control lists and rules about the address formats (to and from headers) that are allowed from specific domains and address ranges. (Those generally also involve queries on tables or directory services, including those like Paul Vixie's RBL (real-time blackhole list: or MAPS, mail abuse prevention system) and it's ilk, like Dorkslayer/ORBS. Recently, MTAs are being increasing required to enforce other policies and implement anti-virus/anti-worm features."
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