All SMTP mail traffic passing through the Exchange server is scanned by Symantec mail Security for Microsoft Exchange (SMSMSE). Individual components of SMSMSE are designed to perform distinct functions, and not all of these components perform hygiene on mail traveling both into (inbound) and out of (outbound) the mail server:
Type of Scan
|Scan for Spam||Inbound messages|
|Scan for Virus and Security Threats||Inbound and Outbound messages|
|Scan for Content violations||Inbound and Outbound messages|
|Scan for Attachment violation||Inbound and Outbound messages|
Several years ago, spammers sent their emails from dedicated mail servers or relayed them through mail servers that were mis-configured to act as open relays. This is no longer the case.
Current spamming techniques use widely distributed "botnets" of compromised computers. Performing spam scanning on all outbound traffic would double the burden that SMSMSE places on a Microsoft Exchange server, without addressing the source of spam as it exists today.