SendMail has a reputation for being hard to configure and has a history of security holes. If you're willing to throw away all that time configuring it, here are some alternatives:

[link|http://www.exim.org/|Exim]
[link|http://www.postfix.org/|Postfix]
[link|http://www.courier-mta.org/|Courier]

I myself use Courier. I haven't tried the other two.

Wade.