Hi,
Well I definitely think that's something you should fix on your end :-(
If the email is automatically removed that means there is a setting somewhere which does it.
You may have automatic rules set on your mail server / mail configuration or somewhere else.
Or maybe the bounce handling is enabled in AcyMailing?
As regards the "you're not authorized" you should definitely take a look on Google, you'll probably find more information about it 😉