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Exchange Anti-Spam Toolkit Using Exchange Anti-spam filtering with QSS Exchange Connector

Exchange anti-spam filtering is supported for mail delivered to Exchange via POP3 download by QSS Exchange Connector. Where possible, anti-spam filtering should be performed during the initial SMTP session (i.e. by the POP3 server). Filtering by Exchange is supported, however correct configuration is required, and it is important to understand the differences in the mail flow in this scenario.

If mail which is downloaded via POP3, then delivered to Exchange by QSS Exchange Connector is filtered by Exchange, Exchange may reject the message. By default, QSS Exchange Connector leaves messages on the POP3 server if they are rejected by Exchange.

QSS Exchange Connector can be configured to delete messages from the POP3 server if Exchange rejects messages (with specific SMTP response codes). The option Delete messages rejected with specific SMTP response codes needs to be selected on the SMTP Delivery tab.

QSS Exchange Connector will need to be configured with an appropriate list of SMTP response codes for this type of processing. We recommend using the following response codes:

  • 553 5.7.1
  • 554 5.7.1
  • 553 5.7.9
  • 554 5.7.9
  • 553 5.1.0
  • 550 5.7.1
  • 550 5.1.0
  • 554 5.1.0
  • 550 5.7.9

Note that QSS Exchange Connector will send a non-delivery report to the sender in this scenario. Sending NDRs due to spam filtering is not an accepted practice. Anti-spam filters are intended to reject messages during the SMTP session. In a POP3 download scenario, this is not possible because the SMTP session has already ended. The difficulty is that the real sender of the message is not known once the message has been accepted (spam frequently contains forged From addresses). We do not support generating NDRs, because an NDR to the From address is likely to propagate accept-then-bounce backscatter spam, which can cause your own mail server or domain to be blocked.

Therefore, filtering of mail delivered to Exchange via POP3 download effectively means that the Reject action specified in Exchange anti-spam filters will be treated as Delete.