Hello @eXch Support please note that I had the same issue that Cricktor had.
Some emails didn’t go through.
Here is a sample screenshot of the issue:
That's Proton Mail blocking your message from being sent. Have you used this email for anything else before? They really don't like it when you only send outgoing messages. Especially if you are a free account.
To me, this even looks as if Protonmail blacklisted the exch.cx domain. There is no reason for them not to allow sending emails from their server unless they want to be connected to a blocked domain.
Maybe that pushed eXch the move to a .net domain.