Why is my email bouncing with a ’550 Relay Not Permitted’ error?

If you receive a “550 Relay Not Permitted” error when trying to send or receive email, this generally means that the mail server has refused to relay the message. There are several possible causes, depending on how your domain and email service are configured.

SMTP authentication

If you see this error when sending email from an email client, such as Outlook, Apple Mail, Thunderbird or a mobile device, your outgoing mail server may not be authenticating correctly.

Please check that:

• SMTP authentication is enabled for your outgoing mail server.
• Your SMTP username is your full email address.
• Your email account password is correct.
• You are using the correct SMTP server and port for your email service.

For our standard email service, the recommended outgoing mail settings are:

• SMTP server: mta.extendcp.co.uk
• Port: 587
• Security: STARTTLS
• Authentication: Required

Port 465 with SSL/TLS can also be used where supported.

Port 25 blocked by your ISP

Some Internet Service Providers block or restrict outbound connections on port 25 to prevent spam.

If your email client is configured to use port 25, try changing the outgoing SMTP port to 587 and make sure SMTP authentication is enabled.

Recently changed DNS or transferred domain

If you have recently changed your domain's nameservers or moved your email service to our servers, there may be a temporary period where different mail servers have different DNS information.

For example, the domain's MX records may have been changed to point to our mail servers before the domain transfer or DNS changes have fully completed. During DNS propagation, some remote mail servers may continue using the previous mail routing information.

This situation normally resolves once the DNS changes have propagated and all mail servers are using the updated information.

Email forwarding loops

A 550 Relay Not Permitted error can also occur if an email forwarding address has been configured in a way that creates a forwarding loop.

For example:

[email protected] → forwards to [email protected] → forwards back to [email protected]

This can also happen when an autoresponder or other automated mail function is configured to forward messages back to an address that ultimately forwards them back again.

Check the forwarding and autoresponder settings for the affected addresses and make sure that messages are not being sent back to the original forwarding address.

Still receiving the error?

If you have checked the above settings and are still receiving a 550 Relay Not Permitted error, please raise a Support Ticket with our Customer Services team.

Where possible, include the complete bounce-back message, as this can contain additional information that will help us identify why the message was rejected.