The message could not be sent because one of the recipients was rejected by the server

Every time you try to send an email you receive an error message similar to the following:

The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was ‘someone@example.co.uk’. Subject ‘, Account: ‘Your Name’, Server: ‘mail.MailServerName.dom’, Protocol: SMTP, Server Response: ‘554 <someone@example.co.uk>:Recipient address rejected: Relay access denied’, Port: 25, Secure(SSL): No, Server Error: 554, Error Number: 0x800CCC79

How to fix

The notable text in this error is Recipient address rejected: Relay access denied’ and it means that you have not enabled SMTP Authentication in your email client.

Enable SMTP Authentication to resolve this issue