A method for data processing comprises: S100. if a to-be-sent email needs to be saved cryptographically or sent cryptographically, automatically converting a main body of the mail into an html file, the html file including an attachment link for linking a mail attachment; S200. compressing a filename of the html file and a filename of the mail attachment into a new html filename and a new mail attachment name using a first open source algorithm based on a first password preset between a sender and a recipient, thereby obtaining a renamed html file and a renamed mail attachment; S300. compressing the renamed html and the renamed mail attachment using a second open source algorithm based on a second password preset between the sender and the recipient, thereby obtaining a compressed file; and S400. releasing a memory space and/or a hard disk space occupied by the to-be-sent mail, encrypting the to-be-sent mail and then saving it to a draft box or sending it in a manner in which a mail has a null mail body and the compressed file is used as the mail attachment. In this way, a method and a system for data processing are implemented, which utilize open source algorithms and have a wider applicability.