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Receiving a Server Error 553 in Outlook When Trying to Send Mail

Troubleshooting Error 553

Error 553 is an email error that is usually caused by a lack of SMTP authentication. When trying to send an email through your local email client, if SMTP has not been authenticated, you might receive a message that looks like this:

The message could not be sent because one of the recipients was rejected by the server. The rejected e-mail address was ‘’. Subject ‘test’, Account: ‘’, Server: ‘’, 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: 0x800CCC79

Many mail servers, including our own mail servers, require SMTP authentication to properly relay emails. To fix this, you just need to enable it.

Start by opening the properties on your local email client. If you’re using Outlook, you can follow these steps to enable SMTP authentication:

  1. From the “Tools” menu, select “Account Settings”
  2. After selecting your email account from the list, click the “Change” button, and insert your server’s name into the form field marked “Outgoing mail server (SMTP)”.
  3. Click on “More Settings…” and select the “Outgoing Server” tab on the new window that opens.
  4. At the top of the Outgoing Server tab, check the box labelled “My outgoing server (SMTP) requires authentication” and make sure “Use same settings as my incoming mail server” is selected.
  5. When you’re finished, click “OK” and close out of the Account Settings window.

Once you’re SMTP authentication is set, you should now be able to send emails without receiving the Error 553 message. If you need further instructions on setting up SMTP in Outlook, check the official Outlook 2016 Documentation.


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