Refresh                                                                                                                                                                             

This is the reason i think people should sit a test before they are allowed to use a computer. I think that emails advising an email has been marked as spam should have a link marked "ID10T". Whenever anyone incorrectly marks an email as spam and you get the message back from your ISP you click the link and their account is disabled for 24 hours.
What is worse when you get all these incredibly stupid computer users put together in a building, given a pompous job title and positions of self importance.   they then ring up IT with a problem that to them will rival the end of the world, like they can't log on and it turns out they have the caps lock on while they type their password. It baffles the mind how these people mange to get themselves dressed in the morning never mind do the job they do.                                                                                                                                                                             

Bump all good here Matt                                                                                                                                                                              

Thing is... when I email or PM these people a 'warning' that they must stop or I'll have to remove them from the site... they then kick off with me, denying all knowledge of ever clicking on "Mark as Junk".  THEN they threaten to report me to Hotmail.   I tell them "Go ahead, and here's the email warnings that Hotmail sent to me about your actions".

Nobs with a capital F!!! 
                                                                                                                                                                             

I've had similar issues with some of the sites I run at work. We found that if you register as a bulk-emailer with the likes of Yahoo! (who also run the mail-servers for BT & its wholesale customers) it decreases the chances of you being treated as a spammer.

We also found that it helps to stop mailing inactive users.

already done.  I'm registered as a bulk sender with google also.  I even take part in their Feedback Loop thing, so I get emailed when someone flags as email as spam (and then I remove them from the site to prevent them further harming our reputation).