In iOS 3.x, people complained about the lack of mail batch deletion option. The only way back then was to swipe and delete each and every emails in your inbox.
In iOS 4.x, Apple introduced their batch mail deletion options. You tap edit, and you will have to tap the emails you wanted to delete. But it is still not enough. If you are like me, with mail box flooded with tons and tons of junk mails, this feature introduced by Apple is not enough. It’s impossible to select 1000 mails if you have 1000 mails in your inbox.