Exim is a mail transfer agent (MTA) that can be run as an alternative to Sendmail on Unix systems.* Exim is open-source software that is distributed under the GNU General Public License (GPL), and it runs on all the most popular flavors of Unix and many more besides. A number of Unix distributions now include Exim as their default MTA. I wrote Exim for use on medium-sized servers with permanent Internet connections in a university environment, but it is now used in a wide variety of different situations, from single-user machines on dial-up connections to clusters of servers supporting millions of customers at some large ISP sites.

The code is small (between 500 KB and 1.2 MB on most hardware, depending on the compiler and which optional modules are included), and its perfor mance scales well. The job of a mail transfer agent is to receive messages from differ ent sources and to deliver them to their destinations, potentially in a number of differ ent ways. Exim can accept messages from remote hosts using SMTP† over TCP/IP, and as well as from local processes. It handles local deliveries to mailbox files or to pipes attached to commands, as well as remote SMTP deliveries to other hosts.

Exim consists of support for the new IPv6 protocol in its TCP/IP functions, as well as for the current IPv4 protocol. It does not directly support UUCP, though it can be inter faced to other software that does, pr ovided that UUCP ‘‘bang path’’ addressing is not requir ed, because Exim supports only Internet-style, domain-based addr essing.

Download Exim The Mail Transfer Agent

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