Verified answer

These are solutions for deleting stuff from inbox.

1: Put everything you want to delete in the trash then press delete

2: Try to put stuff you want to delete in the Spam section and press empty

3 :Manually select the stuff you want to delete in your inbox, then in actions press delete

Those are the only ways you could delete stuff from mail, correct me if i'm wrong. If all well doesn't work then just make a new email. No harm done.

Cheers