This articles describes how to fix the Unable to Move Message. The message could not be moved to the mailbox Trash. error on the iPhone IMAP account when deleting a message.

 Unable to Move Message Error

Instructions on modifying IMAP settings
  1. Press the Home button and choose Settings.
  2. Scroll down and click Passwords & Accounts.
  3. Tap the name of your IMAP email account.
  4. Scroll to the bottom and click Advanced.
  5. Scroll to the bottom and tap the empty IMAP
    Path Prefix
    . Enter INBOX in capitals
  6. To save and close the settings, click Accounts at the top left and click Done at the top right twice

Note: If you can't see the Advanced button or the IMAP path prefix, you will need to re-create your IMAP email account. Read the Knowledge Base article on How To Configure IPhone To Connect To Exchange Mailbox Using IMAP (Exchange Hosting) for more inforamation.