I hope that this might help anyone who has a problem as I did on both an iPhone 6 and 5S. I am on iOS 9.2.1 on both. On setting up a Plusnet imap account on both phones I found that I could send and receive emails OK but when I tried to delete from the Inbox I got a pop up screen saying 'This message could not be moved to the mailbox Trash' and with an OK aknowledgement button. When you hit OK the message seems to have gone from the underlying Inbox screen but if you go out to another mailbox and then back into Inbox the 'so-called' deleted message is back in there. I tried moving the mail to Trash first and then deleting but the same thing happened. There is no problem with a Plusnet POP account or Google mail. After hours on the phone being passed through Apple first level support and second level (who suggested that it was a Plusnet server response fault) and trying Plusnet support (who suggested it was Apple mail not having the correct settings) Apple second tier support found this fix which I hope may be useful:-
1. Settings
2. Mail, Contacts, Calendars
3. Select your imap account
4. Select Account
5. Scroll down and select Advanced
6. Scroll down to IMAP Path Prefix and select to edit
7. Edit to add the word INBOX (Must be in capitals, lower case and mixed case does not work)
8. Select Account at the top LHS of screen
9. Select Done at top RHS of screen
That sorted the problem for me. Hope it is of some use to others that might be getting the same problem.
Roger
