7. The email system of claim 5 , wherein: an original sending function of the email client is replaced by the tag composition engine, and when a user clicks a send button to send the email, the tag composition engine translates texts in various styles into contents with corresponding tags, and then calls the original sending function of the email client.
5. The email system of claim 1 , further comprising: a tag composition engine for inserting the tags into the email contents according to the tag related information kept by the content style setting component.