When IPv6 is disabled for Exim, no IPv6 activities take place. AAAA records are never looked up, and any IPv6 addresses that are listed in local_interfaces, data for the manualroute router, etc. are ignored. If IP literals are enabled, the ipliteral router declines to handle IPv6 literal addresses.
1. Navigate to the Exim configuration Manager (WHM > Service Configuration > Exim configuration Manager)
2. Click on Advanced Editor
3. Scroll down to where you can click the button that says "Add additional configuration setting" (it's just above Section: BEGINACL")
4. Select disable_ipv6 and type true in the box next to it: