If you are getting the error "Unable to move message. The message could not be moved to the Trash," please peform the below tasks:

1. Go To Settings Icon
2. Click on "Mail, Contacts, Calendars"
3. Click on your email account.
4. Click on the Account Link
5. Scroll to the bottom and click Advanced
6. Under the "Mailbox Behaviors" listing at the top, select "Drafts Mailbox"
7. In the new window, select the "Sent Mailbox" folder. From the "On the Server" listing in the lower portion of the window, select the "Sent" folder. You should see a check mark next to this folder. Do NOT check the "On My iPhone" "Sent" selection at the top
8. Click the "Advanced" button on the top left to go back to the advanced page.
9. Click the "Deleted Mailbox".
10. Click the folder named "Trash" folder under the "On the Server" portion. Note the iPhone trash at the top, and not any other named folders (like "Deleted Messages", "INBOXTrash", etc..)
11. Click the "Advanced" button on the top left.
12. Click on "Account Info".
13. Click "DONE" (do not click Cancel).

You may need to then restart your iPhone, but turning it off and back on.