A system, a server, a method, and a computer program are described for relaying an electronic mail without a leak of secret information included in a quoted electronic mail to an unintended recipient without impairing the usability of the electronic mail system. The server receives an electronic mail that is newly created by one of the clients with quotation from one or a plurality of electronic mails received in the past. The server determines, for each quoted electronic mail quoted in the received electronic mail, whether a destination designated in the received electronic mail is included in an originator and a destination set in each quoted electronic mail. The server edits the content of each quoted electronic mail that is determined not to include the destination designated in the received electronic mail. The server transfers the electronic mail including the edited quoted electronic mail to the designated destination. The server stores edition information for returning the edited quoted electronic mail to a state before the editing in association with information that identifies the received electronic mail.