How to fix spam notifications

What does a Spam Notification bounce mean?

A Spam Notification occurs when a receiving mail server rejects the message completely, thinking it is spam. In these cases, the email is not delivered to the recipient at all (not even to the spam folder). This often happens if a recipient you send to's mail server is using an aggressive spam filter, such as Barracuda or Mimecast. Something in the content could be causing the spam filter to flag the message or it could just be that the recipient's domain blocks all inbound messages that are not specifically whitelisted.

If you expand the bounce information using the More Details button, you can sometimes get a bit more insight into why the spam filter blocked the message.

For example:

Final-Recipient: rfc822;
Action: failed
Status: 5.0.0 (undefined status)
Remote-MTA: dns; (
Diagnostic-Code: smtp;550 permanent failure for one or more recipients (

X-PowerMTA-BounceCategory: spam-related

Occasionally the bounce details will also include a link to a URL that provides additional details around what the bounce code means for that specific spam filter.

How do I fix it?

Spam Notifications need to be resolved on the receiving side, specifically with the spam filter settings for the domain you are sending to. To resolve the blocks, contact the recipient through another channel and ask them to ask their IT team or mail administration team to whitelist either your sending domain or Postmark's sending IP addresses in their spam filter settings.

If they choose to whitelist Postmark's sending IP addresses, provide them with the following ranges:

  • ( - 127)
  • ( - 255)

Note: Addresses that bounced due to a Spam Notification do not need to be reactivated in Postmark before you can send to them. You can send to them again immediately once they confirm they will allow your mail to get through their spam filter.

Last updated October 30th, 2018

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