You can customize how the Content Filter agent assigns SCL values by configuring custom words. Custom words are individual words or phrases that the Content Filter agent uses to apply appropriate filter processing. You configure approved words or phrases with Allow phrases and unapproved words or phrases with Block phrases. When the Content Filter agent detects a preconfigured Allow phrase in an inbound message, the Content Filter agent automatically assigns an SCL value of 0 to the message. Alternatively, when the Content Filter agent detects a configured Block phrase in an inbound message, the Content Filter agent assigns an SCL rating of 9.

You can enter custom words or phrases in any combination of uppercase and lowercase letters. However, when the Content Filter agent evaluates message content, it ignores case. The maximum number of custom words or phrases that can be created is 800.

The Content Filter agent also includes Microsoft Office Outlook Email Postmark validation, a computational proof that Outlook applies to outgoing messages to help recipient messaging systems distinguish legitimate email from junk email. This feature helps reduce the chance of false positives. In the context of spam filtering, a false positive exists when a spam filter incorrectly identifies a message from a legitimate sender as spam. When Outlook Email Postmark validation is enabled, the Content Filter agent parses the inbound message for a computational postmark header. The presence of a valid, solved computational postmark header in the message indicates that the client computer that generated the message solved the computational postmark.

Computers don't require significant processing time to solve individual computational postmarks. However, processing postmarks for many messages may be prohibitive to a malicious sender. Anyone who sends millions of spam messages is unlikely to invest the processing power that is required to solve computational postmarks for all outbound spam. If a sender's email contains a valid, solved computational postmark, it's unlikely that the sender is a malicious sender. In this case, the Content Filter agent would lower the SCL rating. If the postmark validation feature is enabled and an inbound message either doesn't contain a computational postmark header or the computational postmark header isn't valid, the Content Filter agent would not change the SCL rating.

In some organizations, all email to certain aliases must be accepted. This scenario can introduce problems if your organization is in an industry that manages significant volumes of spam.

For example, a company named Woodgrove Bank has an alias named customerloans@woodgrovebank.com that provides email-based support to external loan customers. The Exchange administrators configure the Content Filter agent to set Block phrases that filter out words or phrases that are typically used in spam that is sent by unscrupulous loan agencies. To prevent potentially legitimate messages from being rejected, the administrators set exceptions to content filtering by entering a list of SMTP email recipient addresses in the Content Filter agent configuration.

You can also specify senders and sender domains that you do not want the Content Filter agent to block.

In Exchange 2013, the Content Filter agent uses the Outlook Safe Senders Lists, Blocked Sender List, Safe Recipients Lists, and trusted contacts from Outlook to optimize spam filtering. Safelist aggregation is a set of anti-spam functionality that is shared across Outlook and Exchange. As its name suggests, this functionality collects data from the anti-spam safe lists that Outlook users configure and makes this data available to the anti-spam agents on the Exchange server. Email messages that Outlook users receive from contacts that those users have added to their Outlook Safe Recipients List, Safe Senders List, or trusted contacts list are identified by the Content Filter agent as safe. The Sender Filter agent also performs per-recipient sender filtering using the Blocked Senders list that users configure. For more information, see Safelist Aggregation.