1. A method for sending email, comprising: (a) receiving an email address composed by a user, wherein the email address includes a destination domain; (b) while the user is composing another portion of an email message associated with the email address received in step (a), determining whether the destination domain as composed by the user in the email address is located on a list of destination domains that do not accept email, wherein the list of destination domains is stored in computer storage media; (c) if the destination domain is located on the list of destination domains not accepting email, graphically modifying the destination domain of the email address in the email message composition screen to indicate to the user that the email may not be deliverable to the email address; and (d) if the destination domain is not located on the list of destination domains not accepting email, determining whether the destination domain as composed by the user is accepting email by attempting to connect to a destination server associated with the destination domain, and adding the destination domain to the list of destination domains not accepting email if a connection cannot be made to the destination server associated with the destination domain.