title: SMTP Error 535 (Incorrect authentication data) using PEAR mail
body: <p>I used the code from <a href="https://stackoverflow.com/a/2748837">https://stackoverflow.com/a/2748837</a> to attempt to log into both Gmail and my website's server, and for both of them I received the same error:</p>
  
  <pre><code>authentication failure [SMTP: Invalid response code received from server (code: 535, response: Incorrect authentication data)]
  </code></pre>
  
  <p>I have double- and triple-checked that the usernames and passwords are correct (since it works from a desktop client), and removed the brackets around the username. What could be the problem?</p>