Question
You wish to setup a custom MAILHELO of an account on a dedicated IP address. You go to enable the "Reference /etc/mailhelo for custom outgoing SMTP HELO" option an find it is greyed out in the Exim Configuration Manager page.
How can you make the option available?
Answer
The option is being overridden by the "Use the reverse DNS entry for the mail HELO/EHLO if available" option. Disabling it will allow "Reference /etc/mailhelo for custom outgoing SMTP HELO" to become active.
In some circumstances, you will also need to disable the option "Send mail from the account’s IP address". This is mentioned, as this article assumes "Send mail from the account’s IP address" is already disabled. You can see the option in the images of this article.
You can use the following steps to do so:
1. Navigate to the following location:
WHM: Home -> Service Configuration -> Exim Configuration Manager
2. Select the "Domains and IPs" tab.
3. Turn off the "Use the reverse DNS entry for the mail HELO/EHLO if available" option.
4. You can now use the "Reference /etc/mailhelo for custom outgoing SMTP HELO" option.
5. Save at the bottom.