How to Delete the Email History on an iPhone
The iPhone is a smartphone device first brought to the U.S. by Apple in 2007. In addition to browsing the Web, using a wide variety of applications and consuming media on the iPhone, you can also read and write emails. If you're looking to delete your entire email history, there is no "delete all messages" option on the iPhone, but there is a faster way to delete your email history than removing each message one at a time.
Tap the "Mail" icon on your iPhone's home screen.
Press the "Edit" button in the top-right hand corner of your email inbox.
Tap on your mail messages to place a red check mark beside each one.
Press the "Delete" button on the bottom of the screen to delete the messages.
Tap the back arrow that contains your account name, which is located at the top left side of the screen.
Enter the "Trash" folder by tapping on it.
Select "Delete All" to permanently remove the email messages from your iPhone history.