This is not possible on the default version of mail on the phone, but i have downloaded K-9 Mail from the market for Free. This has many more features than the standard version, and one of those is "Mark All as Read" or you can select a few emails and "Mark as Read". I have intgrated this with Exchange (WebDAV method) and multiple POP3 accounts as well. Works well. The Calendar function of this is not the best, but again this is not a Calendar application, only a mail function, but does have some visibiltiy into the calendar as well. Hope this helps!