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.
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.