Anti-Spam and Antivirus Mail Flow

Anti-Spam and Antivirus Mail Flow

When an external user sends e-mail messages to a Microsoft Exchange server that runs the anti-spam features, the anti-spam features cumulatively evaluate characteristics of inbound messages and either filter out messages that are suspected to be spam, or assign messages a rating based on the probability that the message is spam. This rating is stored with the message as a message property that is called the spam confidence level (SCL) rating. This rating is persisted with the message when the message is sent to other Exchange servers.

Filters are applied in the following order when the Edge Transport server is Internet-facing:

• A SMTP server connects to Exchange Server 2007 and initiates an SMTP session.
• Connection filtering.
• Sender filtering.
• Recipient filtering.
• Sender ID filtering.
• Content filtering.
• Attachment filtering.
• Antivirus scanning.

After all the filters are applied and the message has been scanned for viruses, the message is sent to the intended recipient's mailbox and the Junk E-mail filtering is applied. If the SCL rating for the message is equal to or greater than the SCL Junk E-mail folder threshold, and the SCL Junk E-mail folder threshold is enabled, the Mailbox server puts the message in the Outlook user's Junk E-mail folder. If the SCL value for a message is lower than the values for the SCL delete, reject, quarantine, and Junk E-mail folder thresholds, the Mailbox server puts the message in the user's Inbox.