MyBB Community Forums

I'm not going to bother with messing around with workarounds using other methods. I'm off to ask the hosting about this now. Thanks for the help you provided here in the meantime.

The hosting support forums themselves are running MyBB so hopefully there's a good reason why my MyBB forums on their hosting isn't working with mailing with MyBB.

In your communication with your host, provide the test script. If you mention that mail isn't working for MyBB, they will probably tell you it's a MyBB issue which is not.