When sending an email, your message may fail and return with SMTP Error 551 if the recipient’s address is no longer valid or has been moved to a different mailbox or domain. The receiving mail server returns this error to indicate that it recognises the destination domain but cannot deliver the message to the specified recipient.

Understanding this error is essential to prevent repeated delivery failures and to ensure your emails reach the correct users. SMTP Error 551 is usually considered a permanent failure, which means the mail server will not automatically retry delivery. Action is required before the message can be sent successfully.

How to Resolve SMTP Error 551

1. Confirm that the recipient’s email address is typed correctly and includes no spelling errors.

2. Contact the recipient to verify whether their email address has changed or has been migrated.

3. Check whether the address is an alias that may have been removed or disabled.

4. Update the recipient address in your address book, CRM, or mailing list.

5. If you manage the recipient domain, login to cPanel and confirm that the mailbox exists.

6. Resend the email only after confirming the correct destination address.

Additional Information

• SMTP Error 551 often occurs when an email address has been retired, but is still referenced in contact lists or automated systems.
• Some mail servers use this error code to indicate that the recipient has moved, but they do not always provide forwarding details.
• Continuing to send emails to invalid recipients can negatively affect your domain’s sender reputation over time.
• Mailing lists and CRM systems should be cleaned regularly to remove addresses that generate permanent SMTP errors.
• If multiple recipients at the same domain return this error, the issue may be related to changes on the receiving server.
• Most email clients will not retry delivery automatically, because Error 551 is treated as a permanent failure.

Login to Domains.co.za Account

1. Go to the Domains.co.za website Account Login page.

2. Enter your Email and Password and click the Sign In button.

3. You will see the Domains.co.za Dashboard, displaying the Manage Account menu on the left and your Account Information, Account Overview and Open Support Tickets on the right.