When CoreBridge cannot deliver an email, you receive an email delivery problem notice. The Type, Reason, and Detail lines describe what happened. CoreBridge does not block the address. The recipient, or their mail server, does.

What each type means

Permanent refusal (hard bounce): the address is invalid or does not exist, or the server refused the sender or the content. Correct the address if it is wrong. If the address looks right, the recipient's mail administrator needs to allow the message. A Reason of bad mailbox, with a 550 blocked detail, means that mailbox was permanently refused. Sending the same message again does not clear that refusal.

Temporary deferral (soft bounce): the mailbox is full, the message is too large, the server is briefly unavailable, or there is a temporary hold. Try again later. The recipient may need to clear that on their side.

Spam report: the message was delivered, then the recipient or their mail provider reported it. Confirm this is someone who expects email from your business.

Not sent (reject): delivery was not attempted. The address is usually already paused from an earlier problem, or there is a problem with the sending domain. The Reason line says which.

What you can do

Compare the Recipient address on the notice with the address on the contact. If it is wrong, correct it and send again. If it is right, the recipient's mail administrator needs to allow the message.