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Microsoft Office 365 Outlook is literally the only business email application that can't add an IMAP account to manage "janedoe@example.com" if the user's account name is just "janedoe", without a hidden trek through the deprecated Control Panel: https://answers.microsoft.com/en-us/msoffice/forum/all/cannot-add-imap-account-to-outlook-if-the-email/97005358-6d77-4986-bd43-4944ee8eb682
No one ever needs to hire me or call me for support to add an email account, unless the program they're adding it to is the current Outlook. Not even older, pre-365 versions of Outlook were missing this absolutely critical configuration setting.