The next step is a bit scary. Am I smart enough to let procmail do all of this for me? In that case I might consider ditching Perl in favor of munpack, which I saw in Wireless Hacks

Note that if you stick with this script, I'll be able to create arbitrarily named directories as your user simply by sending you mail. (The contents of the From: header are completely untrustworthy - your script doesn't prevent me from placing ../../../../home/bdfoy as my From: header) I'll also be able to create files as your username with pretty much arbitrary content (but I won't be able to overwrite existing files, thanks to the checks in MIME::Parser::Filer). Eventually, this might lead to a compromise. (If you use bash, ask yourself - do you have a ~/.bash_profile file?)

At the very least, I'd add this line right after you get the new parser:

$from = $parser->filer->exorcise_filename($from);
[download]

I'd then have someone go over this script with a fine-toothed comb for security issues before invoking it automatically on arbitrary data sent over the network. (Which is what mail messages are)