ServerWatch: qmail Mail Server Review

“qmail is an Internet Mail Transfer Agent (MTA) written
by Dan Bernstein for Unix, Linux, and BSD operating systems. As a
replacement for the sendmail system provided with virtually every
UNIX server, qmail functions uses the Simple Mail Transfer Protocol
(SMTP) to exchange messages with MTAs on other systems.

qmail promises four things over sendmail and other MTAs:
security, performance, reliability and simplicity. Being more
secure than sendmail is not a major issue. Sendmail is many years
old, and is known to be very insecure. Performance is enhanced
through the use of a system that allows 20 messages to be sent
simultaneously, while reliability is boosted by the use of small,
yet strictly performing modules that guarantee that once a message
is received, it will get to its designation. Bernstein also claims
that qmail is simpler than any other similarly performing
competitor because it is small.

qmail is in fact much more secure than Sendmail. qmail is made
up of separate modules that each perform a specific task. Each of
the separate modules are paranoid of each other; they each run at
different security levels and do not trust one another to ensure
that they perform correctly. This prevents a malicious user from
taking over the whole qmail system by taking over just one potion
of it. Because each module runs at a different security level, a
malicious user would have to take over each module independently,
which would require access to each level (names and


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