When you send an email and get an “address rejected” error message, it means the email server can’t verify your email address because the SMTP server authentication feature is disabled in your email client.
The full text of this error message looks something like this:
The message could not be sent because the server rejected the sender's email address. The sender's email address was (Email address). Subject: (Subject), Account: (Account name), Server: (Server name), Protocol: SMTP, Server Response: '505 Authentication required', Port: 25, Secure(SSL): No, Server Error: 505, Error Number: 0x800CCC78
To resolve “address rejected” error messages
Enable the SMTP server authentication feature in your email client.
Note: Every email client has different instructions for enabling this feature. You can find instructions for your email client in the client’s online help, or by searching the Internet.