Email

Got a bounce-back (undeliverable) message?

A bounce-back (also called an undeliverable message or NDR) is an automatic reply telling you an email couldn't be delivered. The message usually says why.

Common reasons

• "Address not found" / "Recipient doesn't exist": check the spelling of the address. If it's right, the person may have left, or their email system has a problem. Contact them another way.
• "Mailbox full": the recipient's mailbox is full. They need to clear space.
• "Message too large": send a OneDrive sharing link instead of a big attachment.
• "Rejected", "blocked" or "spam": the receiving system refused your email. This can be a filtering issue at their end, or something we need to check on your domain.
• Delayed delivery warnings: the receiving server isn't responding. Microsoft keeps retrying for a while, so wait before resending.

Is it our end or theirs?

If you can email other people fine and only one address bounces, the problem is almost always with that recipient's email system. They'll need to ask their IT provider to check.

Need us to check?

Raise a ticket and attach the bounce message (or a screenshot of the whole thing, including the technical details at the bottom). That tells us exactly what went wrong.