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

You will got this error when your SMTP server authentication was not selected on your email client.

To solve this.

1. in your microsoft Express go to Tools Menu
2. Select Accounts and locate your mail account under mail Tab.
3. After selecting your email account, click the properties button.
4. Under Servers Tab, Tic My Server requires Authentication.
5. click ok and Finish

The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was ‘email@email.com’. Subject ‘its important’, Account: ‘mail.email.net’, Server: ‘mail.email.net’, Protocol: SMTP, Server Response: ‘553 sorry, that domain isn’t allowed to be relayed thru this MTA (#5.7.1)’, Port: 25, Secure(SSL): No, Server Error: 553, Error Number: 0×800CCC79