System for deferring the delivery of an e-mail sent by a sender to a receiver through a data transmission network such as Internet wherein a Message Transfer Agent (MTA) associated with the sender is in charge of transmitting over the network any e-mail being sent by the sender. The system comprises a retention server for storing the e-mail whose delivery is to be deferred and an authorization server for giving the retention server the authorization to deliver the stored deferred e-mail to the receiver when predetermined criteria are met. The MTA associated with the sender includes a retention enabling program for sending the deferred e-mail to the retention server when there is an indication in the e-mail that it is to be deferred.