I don't think Gmail would be able to block "own" email servers, because how would you tell them apart from company servers or web sites that send out confirmati

I don't think Gmail would be able to block "own" email servers, because how would you tell them apart from company servers or web sites that send out confirmation e-mails or "forgot password" e-mails? They do however require your server to be properly set up, with a correct reverse DNS etc. And Hotmail/Live mail does the same.