There are two main reasons to have LISTSERV do virus scanning:

1. For reasons outside your reasonable control, your SMTP server is not
doing it, or is not doing it well enough. This is more frequent than you
might think!

2. Belt and suspenders. No AV system is 100% accurate, so if you have two
different AV systems checking your e-mail you gain additional safety
(especially since F-Secure uses three independently developed scanning
engines). The performance cost of letting LISTSERV scan incoming mail is
negligible. It is not done through an exit but built into the code. Virus
scanning is generally very efficient for small files like e-mail, even with
F-Secure, which is admittedly one of the slowest products due to its three
independent scanning engines.

I don't know why you think the spam exit is "horrible." It has to work with
any spam filter and the only reasonable way to pass the message to an
unknown third-party spam filter is through a file. This is not very
efficient, but then it is maybe 0.1% of the total processing time if you use
SpamAssassin, which is what most people use...

  Eric