
When trying to open Outlook 2010 after a fresh install on Windows 10, I was receiving the error “Connection to Microsoft Exchange is unavailable”, as well as an error that the .OST file was not valid.
This would cause Outlook to freeze, and if I made it through the freeze, it would show me a prompt to update the Exchange details for my account. Changing the settings did solve the freezing problem.
The Cause: When setting up Windows, I used my email address as the new Microsoft account to log into the machine. Windows oh so helpfully assumed that email was tied to an Exchange account, and auto-created an email profile with Exchange info for that email account.
Every time Outlook opened, the attempt to connect to that “Exchange account” would make Outlook take a looong time to open, freeze things up, and generally make you hate life.
Even if you add other email accounts and make one of the other ones the default, you still can’t delete or modify this oh so helpful account, so Outlook will continue to freeze up.

The Solution: Before changing the email accountsbelow, I converted the log-in account to a local account in the hope that this would remove the need for the Exchange account. I don’t know if this is a necessary first step or not.
If you’re working with an existing .PST file, back it up now.
- Go into Control Panel -> Mail -> Show Profiles, and add a new Outlook profile with the email account(s) you actually want.
- Set up the new mail account with the option to use a new data file. Then make that new account your default Mail account.
- Delete the profile named “Outlook”, as that’s where the broken Exchange account lives.
- Run Outlook again and continue emailing your favourite people.