As you know most of the hosting providers uses SMTP authentication to send emails from their mail servers. Nobody can send emails from their servers without using SMTP authentication. If it is disabled, anybody can use your mail server to send spam emails or any kind of unsolicited emails. So it is always a good practice to enable SMTP authentication to send emails from your mail server.

However, if you require then it is also possible to bypass SMTP authentication for a particular IP address from WHM. Below are the exact steps to do it:
  1. Login to WHM.
  2. Click on Exim configuration Editor.
  3. Under Access list section find Whitelist: Bypass all SMTP time recipient/sender/spam/relay checks
  4. Click on Edit.
  5. Provide IP address which you would like to bypass to SMTP authenctication.
Click Save.