Task '***firstname.lastname@example.org (1) - Receiving' reported error (0x800CCC0F) : 'The connection to the server was interrupted. If this problem continues, contact your server administrator or Internet service provider (ISP).'
Eventually traced the problem to the timeouts associated with the server settings.
Default is 1 minute changed it to 3minutes 10seconds and it now works!!
Took awhile to find out how to change the settings in Outlook 2019 though.
Open Outlook 2019, select File tab, go to account settings, and again account settings, select an email account, select repair, select repair manually, select NEXT, select Let me repair my account manually, select Outgoing mail, now change the Server Timeouts using the slide bar. Select NEXT, Select Done. Repeat for every account. Then Close. Should work now if the timeouts are long enough.
If you make the timeout very long and it still doesn't work then this isn't likely to be the problem.