When using IMAP mail services on an Apple device you may get the following error message when attempting to delete items:
Unable to Move Message: The message could not be moved to the mailbox Trash
This error is due to the way Apple devices handle IMAP mail. The easiest work around is to press the home button on your device and select Settings.
Scroll down to Mail, Contacts and Calendars.
Select your email account and scroll to the bottom until you see the Advanced option.
Scroll to the bottom again until you see IMAP Path Prefix.
Tap this entry and enter INBOX (in capitals). Select Accounts from the top left and click Done twice to close the settings page.
Now when you reopen mail you should be able to delete and move items as expected.