This feature is enabled in WHM by default to verify the existence of the email sender before accepting any messages. Its main purpose is to protect you against spam attacks that are arriving from random locations.
However, some folks use "virtual" email addresses, by that we mean that the email address doesn't actually exist, it is an alias, and that can cause problems. So what you can do is disable it by doing the following:
- Log into http://<ip_address>:2086 with your root password.
- Click Service Configuration, followed by Exim Configuration Editor.
- Uncheck the following two checkboxes under Mail:
- Use callouts to verify senders... (the first entry).
- Verify the existence of email senders.
- Save the settings.
