iOS Mail not syncing with Outlook

I’ve stuck with the built in mail app for my iPhone 7, it works OK for my purposes, most of the time.
Every now and again if I delete or move emails in Outlook on my desktop, they will stay in my Inbox on my iPhone. I will update, refresh, restart all of that and nothing works.
I was removing my Outlook account from the phone and putting it back, but I’ve found an easier way.

1. Make sure the mail app is at the mailboxes screen, where you choose which mailbox or inbox to open.
2. Switch to Settings
3. Tap Mail
4. Tap Accounts
5. Tap Outlook
6. Turn off Mail, go back to Mailboxes and check Outlook has been removed.
7. Switch back to Settings
8. Turn Mail on again.
9. Switch back to Mailboxes and Outlook should be there again and syncnorized with the server.

 
thanks,
Malcolm.