MailChannels Inbound Filtering allows each recipient to set their own mail filtering policy. For example, `firstname.lastname@example.org` may want spam messages to be quarantined, while `email@example.com` may want them to be rejected outright. Recipients can also use policies to block or allow specific senders.
Sometimes, a single message may be sent to multiple recipients, with different mail filtering policies. MailChannels Inbound Filtering can not process different policies in the same transaction (it is impossible to both quarantine and reject the same message). In this case, any recipient with a different policy than the first recipient will receive the following response: `452 4.5.3 Recipient policy mismatch`.
Most mail-sending applications, when they see `452` response, should deliver the message to any accepted recipients, and then send the message to any deferred recipients (recipents with a different policy) in a separate transaction. In most cases, this should be transaprent to the sender, with the possible exception of a slight delay.
If a message has not been delivered due to `452 4.5.3 Recipient policy mismatch`, you may be able to successfully send it by sending to recipients one at a time. If you need further assistance, please open a support ticket by sending a message to firstname.lastname@example.org.