This seems to be a common problem with the Apple mail software in iOS. The solution is easy enough.
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On your iPhone/iPad go to:
1. Settings
2. Mail, Contacts, Calendars
3. Click on your?"Account" (the account you are having this problem with)
(Note: You may have to do this again on the next screen)
4. Scroll down and click "Advanced"
5. Click "Deleted Mailbox"
6. Switch from "Trash" to "Spam" (at the bottom) then back to "Trash" at the top
7. Return to the mail app. You should now be able to delte and move files
NOTE: You may want to try choosing a Trash folder on the Server, and see if that works. That way (if you set your smartphone to the same trash folder) you can retrieve mistaken deletes on either device.
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