“The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was ‘firstname.lastname@example.org’. Subject ‘Teste’, Account: ‘email@example.com’, Server: ‘mail.intergiro.net’, Protocol: SMTP, Server Response: ‘503 This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.’, Port: 25, Secure(SSL): No, Server Error: 503, Error Number: 0x800CCC79 ”
We will get this error even if secure password authentication error is enabled in the server. Mail cannot be send from the server using outlook. This is due to a mis configuration in Mail enable settings.
Mail enable > SMTP (right click) > properties > Relay
Allow Relay For Privileged IP Ranges
Allow Relay For Local Sender Addresses