"The primary issue in spam filtering is not that we don't have training corpora, it's that spammers are very efficient at finding holes in your system." Findin

"The primary issue in spam filtering is not that we don't have training corpora, it's that spammers are very efficient at finding holes in your system." Finding holes on sites like gmail and hotmail is actually much easier than on private sites, because the spammers no doubt have accounts on gmail and hotmail and can test what gets through and what fails and tweak their algorithms until their spam gets through. Spammers don't have that luxury on private servers, so they have to spam blindly. So in this respect private servers have an advantage over gmail and hotmail. On the other hand (as has been pointed out many times in this thread), gmail and hotmail have the advantage of advanced spam detection algorithms and virtually instantaneous feedback from millions of users.