Whilst researching my post on the Microsoft Exchange intelligent message filter a couple of months back, I came across the following message hygiene architectural principles, which Microsoft promotes as best practice:
- Anti-spam filtering must be performed before anti-virus filtering.
- Anti-spam filtering should be performed for inbound mail only.
- Anti-spam filtering should remove messages (cf. quarantining messages).
- Anti-virus filtering must scan both inbound and outbound mail.
- Anti-virus filtering must be mail-direction aware.
- Anti-virus filtering must block messages that it cannot scan.
- Anti-virus and anti-spam filtering system must integrate with Exchange Server.