Help please! Can't delete email from iPhone6

This just started happening a week or so ago. I try to delete messages from my inbox, and it appears successful. But then I get a notification that "Messages cannot be moved to Trash." I'm doing nothing differently than before. I've tried going into settings/accounts/advanced and checking that messages are set up to go into the appropriate folders. I've turned off mail and turned it on again. I've turned off the phone and turned it on again. Because I get so much junk mail (up to 50 per day), my mailbox is getting out of control because I can't send email to trash. Please help. This is so frustrating.