Open Outlook or Outlook on the web
Go to Settings or File
Open Mail settings
Find Delegate access or Account permissions
Add the person you want to delegate to
Grant the required permissions
Save the changes
If using Outlook desktop, go to File
Select Account Settings
Select Delegate Access
Click Add
Choose the user from the address book
Set permissions for Calendar, Inbox, Tasks, and Notes
Confirm and save
If using Outlook on the web, open Settings
Select Mail
Select Accounts
Select Delegate access
Add the delegate
Assign permissions
Save
If mailbox access is needed, assign Full Access in Microsoft 365 admin center
If sending as the mailbox is needed, assign Send As permission
If sending on behalf is needed, assign Send on Behalf permission
Wait for permissions to sync
Have the delegate restart Outlook or sign out and back in
Test access by opening the shared mailbox or sending a test email