The lists of safe senders, safe recipients, and blocked senders are all last-step controls to message hygiene on the client. Safelist aggregation extends the reach of client configuration to an Exchange 2007 transport server. For example, neither the Edge Transport server nor the Hub Transport server with the antispam agents installed need to waste resources filtering a message in which the sender's email address is included in the recipient’s Contacts folder and resides in their safe recipient list.

Don’t confuse safelist aggregation with server sender and recipient filtering for Exchange 2007. Information in safelist aggregation is verified during the Content Filter process, which reduces the instances of false positives because the server hygiene filters are using more specific information from the clients.

Safelist aggregation isn’t an Outlook 2007 setting, but it’s certainly a benefit of using Exchange 2007 with Outlook 2007. Safelist aggregation represents a compilation of safe SMTP addresses and safe domains listed in the safe senders and safe recipients lists for a mailbox. The sum of these entries for a mailbox is called a safelist collection, which holds a maximum of 1,024 unique entries. You can implement safelist aggregation per mailbox by executing the Exchange Management Shell command:

\[PS\]> Update-SafeList  -Identity
\[-DomainController \] \[-Type  \]

which takes the safelist collection data from mailboxes and places it into hashed entries stored in the AD record for the account that owns the mailbox.

From there, the local Hub Transport accesses the content for filtering. That data can also be part of an Edge Synchronization subscription to allowing the Edge Transport Server to access safelist content through Active Directory Application Mode (ADAM). When users make changes to their safelists in Outlook, those changes are not automatically applied to safelist aggregation. You can schedule the PowerShell command to implement safelist aggregation at regular intervals to maintain current information for server-side content filtering.

Encourage users in your organization to maintain accurate junk email whitelists and blacklists. By doing so, they can add value to the overall performance of message hygiene in the Outlook 2007 and Exchange 2007 enterprise.