A: The mapping between Active Directory (AD) user and Exchange mailbox is one to one. However, various solutions exist that enable users to have multiple email addresses and even have access to separate mailboxes.
If the user just needs different aliases, which, for example, means email can be sent to firstname.lastname@example.org, email@example.com and even firstname.lastname@example.org, then all that is required is to change the properties of the mailbox and add multiple email addresses using the E-Mail Addresses tab.
If the user actually needs separate mailboxes, then the solution is to create a new AD user account that would actually own the new Exchange mailbox, then disable the AD account for that new user.
Right-click the mailbox, and select the Manage Send As Permission to let the primary AD user send as this new mailbox or the Manage Full Access Permission to give the primary AD user full access to the mailbox (see the screen shot below).
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