When moving or deleting an email on your iPhone you get the error:
Unable to Move Message: The message could not be moved to the mailbox.
- Press the Home button and tap Settings.
- Scroll down and tap Mail, Contacts, Calendars.
- Tap your email account.
- Scroll to the bottom and tap Advanced.
- Scroll to the bottom and tap the empty IMAP Path Prefix.
- Enter INBOX in capitals.
- Press the Home button and then re-open Mail.
- You can now delete / move your emails as normal.