Please be aware that each version of Apple Mail may have variations for how these directions work. These directions should definitely work for Mac OS Monterey 12, Ventura 13, and Sonoma 14.
1) In Apple Mail go to "Mail → Accounts..."
2) An Internet Accounts page will come up. Select on the Account you wish to remove. In this case we want to remove the account "O3265 Exchange".
3) Clicking on "O365 Exchange" brings up a details window which will look like this:
4) Click on the "Delete Account..." button to delete the email account in question.
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