Postfix and qmail are both written with security in mind. There are much fewer exploits for them than sendmail. I prefer Postfix, I find it easier to understand the configuration. However, not enough to replace a working qmail installation. Sendmail I find hard enough to configure, that I either refuse to accept responsibility for administration or would quickly convert. Postfix is several programs, so it can't be compromised in one gulp. Most can run non-root, in a chroot jail, so even it they are cracked, the attacker doesn't get much. The configuration file is readable, even if you haven't read the docs. IMHO, Jeffrey Quoting Robert Barish <bob@bmtsolutions.com>:

Hello Everyone: I have a quick question. I am currently using SuSe 7.3 and sendmail for my email server. I have configured sendmail and been using it just fine. But I was wondering if maybe there is other viable email servers out there to replace sendmail. I would love to hear your recommendations on other alternatives and why. Bob

-- I don't do Windows and I don't come to work before nine. -- Johnny Paycheck