Systems and methods for reducing the number of challenge messages that are sent in response to an incoming message in situations where the incoming message is likely not unsolicited. The systems and methods include evaluating the behavior of a sender with regard to one or more federated messaging services and determining if the sender is approved or unapproved. If the sender is approved, the incoming message is deliver to a recipient's inbox without issuing a challenge message. Unapproved senders are required to respond to a challenge message.