If you’re getting the message above, it’s simply because by default, iPhone wants to use the Trash, Sent and Draft folders on the phone rather than the same folders on your mail server.
What this means is when you try to delete a message, you get an error saying it can’t be moved. For whatever reason, iPhone does not allow you to throw email away in your phone’s trash.
This defeats the purpose of IMAP, which is to completely map ALL folders on the server to each of your email devices. To fix this is very simple.
Follow these steps:
- Go to the iPhone Settings
- Tap on Mail, Contacts, Calendars
- Tap on the email account you wish to edit
- Scroll down to Advanced
- Under the header ‘Mailbox Behaviors’, tap on each of the three mailbox folders and check off the identical box under the ‘On the Server’ header.