I think the marking only works in the beginning, when the program ist set to 'learn'; or at least it doesn't learn fast enough later, once it's set.

There should be the possibility to put the addresses in question on a white list, that means that your provider knows it's a friendly address and no spam. Depending on if you work with the provider directly or if you use an extra programm on your computer for easier access, it'll be found either on your account page or in the 'settings'.

Try google. It knows an answer to every problem.