The way the UNIX OS is designed, viruses are not much of a problem (versus MS OS variations where viruses are very much a problem); hence you will not find much on UNIX viruses, nor should you worry about it very much.
For anti-spam, the built in anti-spam features in the new releases of sendmail work quite nicely.
Also, check of this IEEE paper on email bombs and countermeasures:
http://www.silkroad.com/papers/html/bomb/