Whether or not you or I believe Borderware's amazing claim that it filters 98% of spam using reputation alone, it's clear that reputation is increasingly important.
No surprise there, but what's the implication on legitimate email users?
As more and more spam filtering relies on your reputation as an email sender, your reputation gets more and more important. Lest we forget, most spam is sent by malware-infected zombies, some of which could be on your network.
That's why outbound spam filtering is increasingly important. It's not just about being a good 'net citizen -- you need it to protect your reputation.
If you don't keep a lid on spam exiting your network, your reputation will be trashed. In crude terms, your outbound IP addresses will be blacklisted, meaning your ability to send email to your legitimate business contacts will be severely limited.
If a few of your users are unwittingly sending spam, then all of your users will have serious trouble sending legitimate email.
Of course, an outbound spam filter can't, by definition, use sender reputation. It has to rely primarily on content filtering. Those that claim that reputation is the be-all-and-end-all of spam filtering are missing an important point.
With thanks to Proofpoint's Andrew Lochart and David Stanley, for a stimulating conversation last week.