To get to this page, go to Settings → Anti-virus → Outgoing Messages
This page lets you configure how VPOP3 deals specifically with virus scanning outgoing messages.
VPOP3 will scan outgoing & locally sent messages as well as incoming messages. It will block users from sending messages containing infected attachments. There is no way to disable that behaviour.
The Inform Main Administrator of Virus tells VPOP3 to tell the VPOP3 Main Administrator that someone tried to send a virus, so they can check out that user's computer.