Actually it does work out of the box.
Please read the installation notes.
In order to see any difference you need to activate SPF specifically.
The problem as documented is most servers send emails from a different IP then the one the sites resides on. Thus causing problems.
Now Xmail sends emails from the site IP not the main server IP.
That is what it does. It is a simple program that initiates a socket connection to the destination server bypassing the internal emailing service to ensure the email is sent from site IP.
Now this makes your emails seem more genuine when SPF records do not authorize any IP to be able to send email like the main server IP.
But even if SPF records are missing on a reverse check the email IP coincides with domain IP so email is granted a pass from email providers.
P.S. The CCL was just a bit of text we forgot to change.
It was fixed now.