I've hosted side projects on Hetzner for years and have never experienced anything like that. Do you have any references of projects to which it happened?
They offer unlimited bandwidth with their dedicated servers under a “fair usage” policy.
The bandwidth costs would be higher than what you pay monthly, so they would simply drop you.
You are probably using very little bandwidth, so it doesn’t matter in your case.
However, I assume Jmail consumes a very large amount of bandwidth.
But not because of being "not a profitable customer". Mind sharing some links here?