If
this program works in your situation (and I've never understood the deeper intricacies of how mail servers really work) it will fix your problem.
It enables you to check you mail waiting at the server, and if you don't like what you see, you can delete it at the server without ever having to download it. You can also bounce the offending emails in the faint hope that your address will be flagged as a non-existent one and possible be removed from the list. Even if that doesn't happen, you continue to have the option of killing of the unwanteds without them ever getting in your inbox.
The only downside is that you need to 'train' the program to recognise the "good stuff", and this can take both time and patience.
I've used this one for many years. I will
not download mail without using it first.
Regards,
F_O_R