You should be able to remove the surplus accounts from 'Favorites'by right clicking > Remove.
You should also be able to rename the account in Account Settings.

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Graham Mayor - MS MVP (Word) (2002-2019)
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Thanks for that recommendation, as I've made good progress with it! I was able to remove one of the two duplicate email addresses in Favorites, and when checking under Account Settings>Email Accounts, there are no longer any numbers like (1) and (2) after that email address anymore. But there is still the one duplicate email address under Favorites, and when I do the right click that you've recommended to close it, the option to close that email address in Favorites is grayed out.