You receive a Delivery Status Notification (Failure) bounce email and want to know whether something is wrong with your domain or DNS. Start by reading the error line in the bounce message.
Mailbox does not exist. If the error says ‘Address not found’, ‘Invalid Recipient’, or ‘User unknown’, or shows status 5.1.1, the receiving mail server is reporting that the mailbox does not exist. This is on the recipient’s side, and nothing on your domain needs to change. The usual causes are a typo in the address or the person moving to a different mailbox. Confirm the address with someone else on the thread and resend.
Policy or authentication errors. If the error mentions policy, spam, SPF, DKIM, DMARC, or ‘unauthenticated’, forward the bounce to support so your domain’s mail records can be checked.