In this Exchange Server 2016 article, I’ll show you how to assign Full Access and Send-As Permissions on a Mailbox using Exchange PowerShell.
To get started, Open Exchange EMS and run the cmdlet below (change Names as needed) to set Full Access Permissions:
Add-MailboxPermission -Identity "mike nano" -User exadmin -AccessRights FullAccess -InheritanceType all -automapping $false
To Set Send-As Permissions use the cmdlet below:
Add-AdPermission -Identity "Mike Nano" -User exadmin -AccessRights ExtendedRight -ExtendedRights "Send As"