If you add an e-mail account to your iPhone you might see “Unable to Move Message” when you try to delete a message. I believe this only happens with IMAP accounts (and not POP3). Here is how to fix it:
- Start the Settings app, then tap Mail, Contacts, Calendars.
- Tap the e-mail account name, then on the next screen tap Account.
- Tap Advanced.
- Under MAILBOX BEHAVIORS, tap Deleted Mailbox.
- There are two sections on this screen: At the top is ON MY IPHONE and underneath is ON THE SERVER. There should be a check mark next to the Trash folder in the ON MY IPHONE section. Tap the Trash folder in the ON THE SERVER section.
- Click the back arrow at the top. You should probably repeat the process for other folders.
- Click the back arrow again, then click Done.