Bounced message — how to read the error¶
When a message cannot be delivered, you receive an error message back (Undelivered Mail Returned to Sender, Delivery Status Notification or similar). The most useful part is a line with a three-digit code, for example:
- Codes starting with 4 are temporary: the platform keeps retrying on its own.
- Codes starting with 5 are permanent: something must be corrected and the message sent again.
Most common errors¶
| Error | What it means | What to do |
|---|---|---|
550 5.1.1 User unknown, No such user, Recipient address rejected |
The address does not exist at the destination. | Confirm the address with the recipient. It is almost always a typo. |
552 5.2.2 Mailbox full, Quota exceeded |
The recipient's mailbox is full. | Let the recipient know by another channel and send later. |
552 5.3.4 Message size exceeds |
The message is larger than the destination accepts. | Send the attachments via a sharing link. |
550 5.7.1, rejected as spam, blocked |
The destination classified the message as spam or blocked the sender. | Review the content and attachments. If it happens again, open a ticket with the full error message. |
SPF, DMARC, not authorized |
The destination does not recognise the sending server as authorised for your domain. | Check you are sending through mail.sooma.com. The administrator should review SPF, DKIM and DMARC. |
Relay access denied |
The receiving server does not accept messages for that domain. | On the destination side, the MX records may be wrong. If it is your domain, see DNS records. |
421, 450, 451 (temporary) |
The destination asked to try later. | Do nothing; the platform retries. You only get a bounce if the destination keeps refusing for several days. |
When asking support for help, forward the complete bounce message (with the technical details), not just the summary.