[Android Central Question]

How do I delete 100s of emails all at once.

[VidJunky]

The easiest way to empty your inbox is online with the provider. Deleting messages on your device can take times and it's not always easy. Depending on what app you're using you might be able to swipe them left and they'll just be deleted as you go, other apps pressing and holding one message enables select mode and then you can select a bunch and delete them all at once, with others you can swipe right to enter select mode.... The possibilities go on and on but we don't know what so you have, what device, how many accounts you're trying to handle, which takes me back to the easiest way is online with your account at your provider. You should be able to log into most accounts thru your browser on your device if that's your only online access. I recommend using the full web version to provide the most options.

[ManiacJoe]

Which phone?
Which version of android?
Which carrier?

Which email service?
Which email app?
Which email protocol (POP3, IMAP, Exchange)?

Assuming that your phone uses IMAP to talk to the server, and assuming the emails are actually stored on the server, I would expect that using a computer to access your emails via a web browser would be the easiest way to do that level of deletes. (Then the phone syncs to the server and the old emails disappear from the phone.)