553 5.7.1 we don't relay mails

A SMTP error code!

553 5.7.1 is a SMTP error code that indicates that the recipient address is invalid or does not exist.

Here's a breakdown of the code:

• 553 is the SMTP error code, which indicates that the recipient address is invalid.
• 5.7.1 is the specific error code, which indicates that the recipient address does not exist.

The full error message is likely something like:

553 5.7.1 Unable to relay mail for [email protected] - No such user here

This error typically occurs when a mail server is trying to deliver an email to a recipient that does not exist on the server or is not a valid email address. The mail server is refusing to relay the email because it cannot deliver it to the intended recipient.

To resolve this issue, you may need to:

1. Check the recipient's email address for typos or incorrect formatting.
2. Verify that the recipient's email address exists on the mail server or is a valid email address.
3. Check the mail server's configuration to ensure that it is set up to relay emails to the intended recipient.
4. Contact the mail server administrator or the recipient's email provider to resolve the issue.