Here's how you can "force" the Mail application to mark all emails as read without jailbreaking (Video)

[youtube]http://youtu.be/CmaqzeXfO5s[/youtube]

  Unfortunately, in Apple's iOS we don't find many options that would ease the process of interacting with some applications, but the jailbreak fully solves the problems. Even so, there are people who don't want to jailbreak to have access to certain functions, so they prefer to forget about them or use various tricks to reproduce them. One of these tricks is presented to us by those from Lifehacker who discovered a method by which the Mail application in iOS can be "convinced" to mark all emails as read, but without selecting them individually.

  All you have to do is press the edit button in the Inbox, select an email, press the Mark button and deselect that email without taking your finger off the Mark button, then release the Mark button and choose the Mark all as option Read. You will immediately notice that all your emails have been automatically marked as read and this without jailbreaking. The trick is very useful for those who receive a lot of emails that they don't read and the good part is that you can reproduce it very easily.

Thanks to UtestMe.