To temporarily fix this issue: Exclude your email domain (or IP address if the message was sent from an on-premises server) ...

  • To temporarily fix this issue: Exclude your email domain (or IP address if the message was sent from an on-premises server) from the spamrl.com block list by filling out the "delist" request at http://spamrl.com.
  • To permanently fix this issue: Contact the recipient and ask them to release the sender's message from their spam quarantine.

Only the recipient or the recipient's email admin can fix this problem permanently. Office 365 support will not be able to help fix these kinds of externally reported errors.