an electronic mail blocking system for reducing undesirable electronic mail that a recipient receives . the electronic mail blocking system filters one or more electronic messages transmitted by a sender having a sender identity to a mail server addressed to a receiver . the electronic mail blocking system comprises comparing the sender identity to an authorized sender list and transmitting the electronic message if the sender identity matches a record within the authorized sender list . the mail server automatically transmits an authentication request containing a question to the sender when the sender identity does not match a record within the authorized sender list . a response containing an answer from the sender in response to the authentication request is compared to a correct answer . if the answer is a correct response to the question , the mail server transmits the electronic message to the recipient and automatically adds the sender to the authorized sender list .