How to edit the backupmxhosts file.

Introduction

/etc/backupmxhosts contains a list of remote servers that will behave as secondary mx hosts for your mail servers.  This allows them to bypass sender rate limits.

Procedure

This file can be modified via WHM at the following location.

WHM >> Service Configuration >> Exim Configuration Manager >> Access Lists >> Backup MX Hosts

Please see the following documentation for more information.

https://docs.cpanel.net/whm/service-configuration/exim-configuration-manager-basic-editor/