Move email messages from an Outlook 2016 Sent Items folder to an outlook.office365.com webmail Sent Items folder?

Tom Cieslik:  That worked great.  To expand on this:
I had already set up a POP account amongst many.  That's where the SENT Items were located in Outlook 2016.
So, I set up a new IMAP outlook.office365.com account in Outlook 2016 per the instructions.
Then I dragged all the Sent Item messages for the one POP account into the Sent Items for the IMAP account.
(Did the same for the inbox for all the incoming messages to that account address).

The one thing that's unfortunate is that the Outlook 2016 Favorites got changed in some strange way.  Some folders remained while others just disappeared.  It's not catastrophic but will require setting up the Favorites again.

Thanks again - big help!

I just found that ALL of my message rules have been deleted.
I wish there were a backup of them.  I don't know if that's possible.

Fred,
If you have rules in outlook -
1. Go to Rules and Alerts
2. Click Manage Alerts
3. Export Rules