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sendmail X is a modularized message transfer system consisting of
five (or more) persistent processes, four of which are
multi-threaded. A central queue manager controls SMTP servers and
SMTP clients to receive and send e-mails, an address resolver
provides lookups in various maps including DNS for mail routing, and
a main control program starts the others processes and watches over
their execution. The queue manager organizes the flow of messages
through the system and provides measures to avoid overloading the
local or remote systems by implementing a central control instance.
sendmail X.0 is intended to be used as a secure and efficient mail
gateway. It does not provide any mail content modification
capabilities, e.g., address masquerading.
Obviously smX is architecturally similar to qmail and Postfix. The
design document:
www.sendmail.org/%7Eca/email/sm-X/design-/main/main.html
Is interesting reading--often comparing traditional sendmail, qmail,
Postfix, Courier MTA, and Exim. Claus Assmann is apparently the lead
designer/implementer. From my first quick read I see a handful of good
ideas--things I wish qmail had/did--as well as a few questionable
decisions. There's some obvious qmail dissing, but, at the same time,
DJB's SECURITY file is included in the design document nearly intact
but without attribution.
The tarball for the Alpha 2.0 release is ten times larger than the
qmail 1.03 tarball, so it's defnitely not as lean as qmail. Claus has
been maintaining sendmail for years, but I don't really have a handle
on his ability to produce near bugfree code.
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