A method, an apparatus, and a system for automatically replying a mail are provided. The method includes: receiving a new mail sent to a user; obtaining presence information of the user; searching for a mail automatic reply message corresponding to the presence information of the user; and sending the corresponding mail automatic reply message to a sender of the mail. Through the method, the apparatus, and the system, the presence information of the user is obtained, and automatic reply messages are respectively set for different presence information, so that the automatic reply messages are associated with the presence information of the user, and when a state of the user changes, the automatic reply messages are not required to be reset, thereby providing convenience for the user.