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He is unable to open 1 Outlook and see both mailboxes and agendas,
Do you mean that you have configured one account in Outlook and cannot add the second email account in One Outlook profile?
If so, we can try the following methods:
1.Click File>Info>Add Account.
2.Click File>Info>under Account Settings, Account Settings...>New.
3.Open Control Panel>Mail>E-mail Accounts.
Hope the above help! If the above is not your issue, please provide more information about your case, such as screenshots about it. (In order to avoid the privacy leakage, please remember to hide your personal information.)
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