Outlook error on trying to change default email account

I have completed uninstalled office 365 and cleared left behind files from appdata and program files and restarted before reinstalling Office 365 incl classic outlook.

Does anyone have any more ideas on how to proceed. I didn't go as far as deleting all left over registry entries related to Office365. And somewhere along the line I must have agreed to storing of outlook setting on my microsoft account as all the email accounts were reinstated on the reinstallation. The only think I can think of is to turn that off and do the clean down and reinstallation again.

kevinboardley said:

I must have agreed to storing of outlook setting on my microsoft account

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You mean this setting?
Information about Store my Outlook settings in the cloud - Microsoft Support

But it's probably because an uninstall doesn't erase your Outlook Profiles.

Are you trying to change the Default to:

Control the "From"?
Change the account used to send email messages - Microsoft Support

Consolidate POP accounts?
Deliver All POP3 Accounts to One Outlook Inbox | Slipstick Systems

Control where your IMAP account Calendar and Contacts are stored?
Using IMAP Accounts in Outlook | Slipstick Systems

You might want to do a test with a new Profile. Add just two accounts and see if you can do whatever it is you are trying to do.
Create an Outlook profile - Microsoft Support

Do NOT delete your old Profiles. There could be data in OST files connected to those accounts that will be lost.

Hi, I'm just trying to reorder mail accounts in the account list and change the default. To either action, that error message is the response.

kevinboardley said:

trying to reorder mail accounts in the account list

Click to expand...

Not sure I understand. You should be able to just drag-and-drop email accounts in the Navigation Bar.

kevinboardley said:

trying to ... change the default.

Click to expand...

I assume you mean you want to change the Default From account for new mail?
Change the account used to send email messages - Microsoft Support

Try a test with a new Profile. Add just two accounts and see if you can change the Default email account.
Create an Outlook profile - Microsoft Support

Do NOT delete your old Profiles. There could be data in OST files connected to those accounts that will be lost.