Error Code: 553 sorry, that domain isn't in my list of allowed rcpthosts

📧 Why Am I Getting This Email Back?

If you're receiving a bounced email with the following error message, it means that your email client is not set up to use SMTP Authentication, which your ISP or hosting provider requires to send outgoing mail.

🚫 Error Message Example

SMTP error from remote mail server after RCPT TO::
host mail.yourdomain.com [64.239.33.14]:
553 sorry, that domain isn't in my list of allowed rcpthosts;
no valid cert for gateway (#5.7.1)
  

✅ How to Fix It in Microsoft Outlook

1. Open Outlook
2. Click Tools > Email Accounts (or Accounts and Services in older versions).
3. Select View or Change Existing Email Accounts and click Next
4. Choose your email account and click Change
5. Click More Settings
6. Go to the Outgoing Server tab
7. Check the box: My outgoing server (SMTP) requires authentication
8. Select Log in using and fill in:
   • Username: your full email address
   • Password: your email password
9. Click OK, then Next, then Finish
10. Restart Outlook

Once SMTP Authentication is enabled, your emails should be sent without issue.