As is known to all, all of the mail system, contains a calendar function, according to the general understanding, E-mail is tool of people's communication, calendar function, is the personal time management tool that seems to be no relationship between, even with the function of "collaboration" in it, it is a part of the calendar function, do not know, the first to write E-mail system, is based on what kind of consideration, contains a calendar function? What a great god can explain?