Scot Finnie's emphasis on scanning outgoing mail is "hard to understand", at least for me...
If the best 2006 antivirus can secure one from being attacked, isn't that means his/her PC is always clean, so why scan mail going out from a known "clean PC" ?
I had a case where a program I was using, that wasn't malware, tried to send out an email without telling me that it was an email I would be sending.
What happened was I was using the Zinio Reader for magazines that I have digital subscriptions to. They are DRM protected files. They have a feature where you can send a friend a free copy of the magazine issue you are currently reading. You click the button and it asks for their email address and a message you want to include.
I thought this would be submitted directly to the Zinio site and they
would send him an invite email. That wasn't what it did though. It tried to silently send an email to my friend from my
pc with a link to get the reader and issue I wanted to share...without telling me it was doing that.
My anti-virus (McAfee at the time) intercepted it and asked my permission to send it...and asked if I wanted to see it first.
I had to see it first...since I don't have a working default email client. It would have failed to send.
I don't like having an email client set as default that other software could have access to. Too many stupid viruses like to mail themselves out to everyone in your address book. Having a default client that has no entries in the address book and can't send mail makes sense to me. I have always done things that way just in case something slips past my AV.
Now as far as an antivirus checking outgoing mail that you send, attachments & stuff, and adding that message at the end...that is for advertising purposes, and to make the recipient of your email think it's clean.
I don't like those messages that get attached to emails from various AV products. Anybody could deliberately send you malware and copy & paste that text from some mail someone sent them and accomplish the same thing...it's misleading and can give some unsuspecting under-educated pc user false confidence.