Question
When formatting the /etc/mailhelo file, what syntax should I use?
Answer
The /etc/mailhelo file contains Exim’s configuration for the HELO command, which initiates dialog between a mail server and a client. This file governs which domain sends the HELO command.
Use your preferred text editor to create an /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