How can I delete all my emails without doing it checkbox by check box? I can't do it from my computer at this time all I have available is my phone. And I don't know how to delete all email at once. Please help my inbox is overwhelming with emails.
Go to Settings => Storage => Used Space => Applications
Find your email app in the list and select it. For example mine is Gmail.
Click on "Clear data". You will get a warning saying you will have to set up your account again. It is your choice if this is what you want to do.
Once you have done this, go back into your email app as you normally would to check your emails and enter your account details. In the Settings of your email app you should set things up not to keep so much email. So for example in Gmail you can reduce "Days of mail to sync" from the default 30 to for example 5.