Getting Rid of Crap in email
Just about everybody uses some kind of weird, screwed up email formatting.
Nobody will just send ASCII anymore -- why oh why?
A quick solution, assuming you already have procmail installed, is using Alex Wetmore's stripmime program.
Once you have it copied somewhere locally and double-checked the perl line at top, just put something like this in your $HOME/.procmailrc file
More complex solutions
A combination of SpamAssassin, MIMEDefang and various Virus filters might work out good with your local sendmail daemon.
Here's a good document to get you started