Sendmail user unknown

The infamous "User unknown" error in sendmail!

The "User unknown" error typically occurs when sendmail is unable to find a valid user account associated with the email address you're trying to send to. This can happen for a few reasons:

  1. Invalid email address: The email address you're trying to send to is not valid or does not exist.
  2. Non-existent user account: The email address is valid, but there is no corresponding user account on the system.
  3. Mail server configuration issue: The mail server configuration is not set up correctly, preventing sendmail from resolving the email address to a valid user account.

To troubleshoot the issue, you can try the following:

  1. Check the email address: Verify that the email address you're trying to send to is correct and valid.
  2. Check the user account: Ensure that the user account associated with the email address exists on the system.
  3. Check the mail server configuration: Verify that the mail server is configured correctly and that the email address is properly routed to the correct user account.
  4. Check the sendmail configuration: Check the sendmail configuration files (e.g., /etc/sendmail.cf or /etc/postfix/main.cf) to ensure that the email address is properly configured.
  5. Try sending a test email: Send a test email to a different email address to see if the issue is specific to the recipient or a general sendmail issue.

If you're still stuck, you can try enabling more verbose logging in sendmail to get more detailed error messages. For example, you can add the following line to your sendmail configuration file:

O DebugLevel=9

This will enable debug logging at level 9, which should provide more detailed information about the error.

If none of these troubleshooting steps help, please provide more details about your sendmail configuration, the email address you're trying to send to, and any error messages you've received. I'll do my best to help you resolve the issue!