Very short answer and totally unsatisfying.
Sorry to hear that you weren't satisfied by the shortness of my answer. I hope that you find the length of this one to be more satisfying.
Can be very simple customized if you change that variable in class_CastMailer.php or class_Mailer.php
It could, but what I was trying to convey was that in the current release, there is no built-in option to do so.
as client we can't do that because your files are encrypted and honest will not be so nice to start to hack you code or to decrypt to sadisfy a simple request
I understand that this comment was mostly intended as provocative jab, but
1) posting in the feature request forum is arguably a better way to get a feature added than making threats in the technical discussion forum, and
2) reverse-engineering the mailer code would be a bit of a waste of time anyway given that our mailer code is open-source