Saying a big 'NO' to SPAM in any format...
The most disgusting material that comes into any emailsystem would be Internet Spam. The acuteness and disgust rate would differ for each spam some just saying 'Get Free Credit Card' to some providing an unwarranted or unethical solicitation. Nevertheless, this presents an enormous waste of Internet Bandwidth for all the servers involved in relaying and delivery of the messages. And it also involves a latent danger of viruses/worms lurking out of them, when an innocent user opens the email.
I came across this nice tool called SpamPal -- a freeware downloadable from http://www.spampal.org/ . Configuration wise, it is quite easy to configure and your email client, communicates to this server rather than your email server. SpamPal opens a connection to the POP3 host, downloads the email, decides a rating on the scale of 1 to 10 and depending upon the severity of the rating, the message is branded with a a header 'Spam' and the subject of the message too is updated.
Now it is upto your email client to decide what to do with this message, wherein which you can create Message Filter rules to optionally divert them to 'Deleted Items' folder or 'Trash them' and send back a false 'Mailer Daemon' to the sender (Autoresponder), if the email client supports them. But be forewarned that spammers do send spam from normal good email addresses too and hence your bounce notification may land into a poor good users emailbox, when he is not involved in any spamming at all.
Technically, SpamPal does a lot of job. After it downloads the message, a few lines from the Internet headers of the message are crosschecked against standard DNS Blacklists in various countries. If a hit occurs, then a rating is updated accordingly, which we have discussed above.
In short, SpamPal is a necessary tool for every desktop, along with the email client to support it combatting spam menace.