If you're using Plesk 8.0 or later, you can set up Dr. Web to be enabled for all new mail accounts. To do this, you have to create an event handler.
Here's the steps you will need:
» Log into Plesk
» Click "Server"
» Click "Event Manager"
» Choose "Mail Name Created" next to "Event"
» In the command area, enter /usr/local/psa/bin/mail.sh --update $NEW_MAILNAME -antivirus inout
» Click "OK"
Thank you for providing an article where Parallel's did only half a job:
http://kb.parallels.com/en/2232
Please note in Plesk 9 the event is called "Mail account created". I would have like this article to also cover the Priority - which is lowest (0) by default, and the user (root?).