1. A method for classifying emails, comprising: acquiring an email composed by a user, a classification tag corresponding to the email, and an identification code corresponding to the email, comprising: determining whether an email classifier corresponding to the email exists; in response to a determination that the email classifier corresponding to the email does not exist: locally creating the email classifier corresponding to the email; and generating the identification code corresponding to the email based on a classification tag input by the user and a creator and creation date for the created email classifier; including the classification tag corresponding to the email and the identification code corresponding to the email in the email; and sending the email to receiving terminals and causing the receiving terminals to classify the received email based on the classification tag and the identification code corresponding to the email, wherein a receiving terminal is configured to: determine whether a locally stored email classifier corresponding to the classification tag and the identification code corresponding to the email exists; and in response to a determination that the locally stored email classifier corresponding to the classification tag and the identification code corresponding to the email does not exist: locally create an email classifier based on the received classification tag and the received identification code; set up a classification rule based on the created email classifier; and classify the received email based on the set up classification rule.