There are two options to create User Mailbox in Exchange Server 2016. You can create mailboxes for users that are already in Active Directory or create new mailboxes that will eventually create associated user account in Active Directory. However you create user mailbox, an active directory user account will be created and the associated mailbox will be created in Exchange server. I already have user accounts created in Active Directory so I will just create the mailbox.
01 – Log on to Exchange Admin Center (EAC) then Click recipients in the features pane.Select mailboxes tab. Click —-> Add and select User mailbox.
02 – Choose Existing user if you already have user account created in Active Directory. If not, you can choose New user and start filling the boxes which will create new user in Active Directory. Click Browse to browse associated user account from active directory.
03 – Select the user account from the list to create it’s mailbox.
04 – Click more option.
05 – Under mailbox database click browse to specify custom mailbox database. Select the database. Click OK. You must create database prior to this step. Click save.
06 – As you can see above, the user account is now created. You can also configure other mailbox types like, shared mailbox, linked mailbox and resource mailbox.