- Open the Settings application.
- Scroll down to Mail, Contacts and Calendars and proceed to tap on it.
- Tap on your IMAP account.
- Tap on Account.
- Tap on Advanced.
- Select the Drafts Mailbox under Mailbox Behaviours.
- Move it from Drafts under On My iPhone to Drafts under On the Server.
- Repeat the same process with Sent...
...and Deleted.
Your mail will now mainly exist on the server, with no discrepancies between your iPhone and other devices.
