Understand a bounce message

Updated 23 September 2026For SmarterMail Build 7692

A bounce is an automatic reply saying your email was not delivered. It often has a subject such as Undeliverable, Mail delivery failed or Delivery Status Notification, and the reason is written inside the message.

Find the reason

Open the bounce message.
Look for the error line. It usually starts with a 3-digit code such as 550, 552 or 554, followed by a short explanation.
Match the explanation to one of the reasons below.

Common reasons and what to do

Address does not exist or user unknown - check the spelling of the address, or ask the person for the right one.
Recipient mailbox full - the other person has no space left. Try again later, or contact them another way, such as by phone or WhatsApp.
Message too large - send a smaller file, or upload it to Google Drive or OneDrive and send the link instead.
Rejected or blocked as spam - see Why your emails land in spam.

If your email never left your outbox at all, that is a sending problem, not a bounce. See Emails won’t send.

None of these fit

Copy the whole bounce message, including the error line, and contact support on WhatsApp at +60 16-916 3324. The full text helps us see exactly where delivery failed.

Common issues

Why did I get an email saying my message could not be delivered?

That is a bounce message. The receiving server rejected your email, and the reason is written inside the bounce. Open it and look for the error line.

My email with a big attachment bounced. What should I do?

Upload the file to Google Drive or OneDrive and send a share link instead of the attachment.

The bounce says the address does not exist, but I typed it correctly. Why?

The person may have left the company or changed their address. Ask them or their company for the right address, then send again.

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