From time to time I check my spam...perhaps it would be better to put it in a spam folder. I believe GMail does this...
I use SpamAssasin to mark spam and then a custom filter to move those things to a spam folder when I download via pop. Effectively doing the same thing you are talking about.
But, it sounds like you are writing an email app? True? My webmail (that I never use) doesn't have a filter I can setup to move marked messages to a spam filter. Or, better yet, it would be nice if I could filter messages in the inbox that were not marked as spam (then I could get to the real stuff much quicker).
I know that SpamAssassin checks dbl.org (or whatever it is) for each message to see the details - probably the exact same thing you are talking about.
Anyays, just waking up so I'm not sure why I wrote all of this.
Good luck...v