Hello,
First, I still love EE. It is very good and I recommended to friend.
I have a problem. I can send email to [email protected] but I can NOT send email to [email protected]. My domain is exemple-alpha.com. I use Gmail (Business) to read my email.
Email are sent. There is no error. But I never receive it.
I read online that there is some “local delivery” switch that could cause some problem in my case. I have no idea how to disable it and to force it to read MX properly. I also read that you are working on email server and already put a list of tutorials. But I think this is “too” much for my need which is just “make php mail function work”.
Also, strangely, my friend use the exact same settings, with [email protected] as email and exemple-gamma.com as domain and everything worked fine “out of the box” (he installed a fresh EE yesterday).
If you can help me, point me in any direction, I will be very grateful 
Regards