How to grant permissions to deleted user's mailbox

Hi BHBDAA,

to authorize permissions for a mailbox of a deleted user within a hybrid Exchange environment (Exchange 2019 on-premises and Exchange Online), you can follow these steps:

1. Reconnect the deleted mailbox:
   Reestablish a connection for the deleted mailbox by associating it with another existing user or creating a temporary user. This is essential as permissions can only be assigned to active mailboxes.
   Connect or restore a deleted mailbox | Microsoft Learn
   
   

2. Grant permissions:
   Once the mailbox is linked to a user account, proceed to assign permissions. The following steps illustrate how to achieve this in Exchange Server:

   • Utilize the Exchange admin center (EAC) or Exchange Management Shell to allocate permissions to the mailbox.
   • The Full Access permission empowers the delegate to open, view, add, and remove contents from the mailbox.
   • If auto-mapping of mailboxes is undesired, employ the Add-MailboxPermission cmdlet in Exchange Management Shell, specifying the Full Access permission with the -AutoMapping $false setting.
   • An example of using the Add-MailboxPermission cmdlet is as follows:

Add-MailboxPermission -Identity "UserMailbox" -User "DelegateUser" -AccessRights FullAccess -InheritanceType All​

Ensure to replace "UserMailbox" with the target mailbox and "DelegateUser" with the designated user.
Add-MailboxPermission (ExchangePowerShell) | Microsoft Learn