Here we will guide you how you can use custom mail ip's and mail helo's
Custom mail IPs and Mail Helos
By default we had given Mail IP's and Mail Helo's enabled to so you dont have to put some efford's for seaching in UI
Mail IPs are built by use so you don't have to touch them or edit them. We arrange it as per the User's IPs. But in case of Mail Helo's we had allowed you to make changes and create a customs mail helo's.
Majorly what you have to do is you have to edit the file /etc/mailhelo as per example given below.
example.com: example.com sub.example.com: example.com example.net: example.net addon.example.net: example.net *: hostname.example.com
The domain and its custom mail HELO are defined in pairs. For example, example.com uses example.com as its mail HELO, sub.example.com uses example.com as its mail HELO, and so on. The last entry, *, is a wildcard symbol that represents every other domain not already listed in
/etc/mailhelo and is considered to be the default mail HELO.