How do I configure mailhelo for Exim?

Question

How do I configure mailhelo for Exim?

Answer

In "Home » Exim » Configuration Manager" you need to adjust two settings.

The first is "Use the reverse DNS entry for the mail HELO/EHLO if available". This needs to be turned off.

The second is "Reference /etc/mailhelo for custom outgoing SMTP HELO". This needs to be turned on.

Then, use your preferred text editor to create a /etc/mailhelo file that resembles the following example:

example.com: example.com
sub.example.com: example.com
example.net: example.net
addon.example.net: example.net
*: hostname.example.com

Source: How to Configure the Exim Outgoing IP Address