Can not send mail 535 incorrect authentication data

The infamous "535 incorrect authentication data" error!

This error typically occurs when your email client or script is trying to send an email using a username and password that is not valid or is incorrect. Here are some common reasons that might cause this issue:

  1. Incorrect username or password: Double-check that your username and password are correct. Make sure you're using the correct capitalization and no typos.
  2. Outdated or incorrect SMTP settings: Ensure that your email client or script is using the correct SMTP settings, including the server name, port number, and authentication method (e.g., SSL/TLS, STARTTLS).
  3. Authentication method mismatch: Verify that the authentication method used by your email client or script matches the one required by the SMTP server. For example, if the server requires SSL/TLS, make sure your client or script is using it.
  4. Username and password are case-sensitive: Some SMTP servers are case-sensitive, so ensure that your username and password are entered exactly as they are required.
  5. Account lockout or password reset: If you've recently changed your password or your account has been locked out, try resetting your password or contacting your email provider's support team.
  6. Firewall or antivirus software blocking the connection: Check your firewall or antivirus software settings to ensure they're not blocking the connection to the SMTP server.
  7. SMTP server issues: If you're using a third-party SMTP server, try contacting their support team to see if there are any issues on their end.

To troubleshoot this issue, you can try the following:

  1. Check your email client or script's logs for any error messages that might provide more information about the issue.
  2. Use a tool like Telnet or a mail client like Thunderbird to test the connection to the SMTP server and see if you can send an email manually.
  3. Contact your email provider's support team for assistance, as they may be able to help you resolve the issue or provide more information about the problem.

I hope this helps you resolve the "535 incorrect authentication data" error!