The user 'insert user here' cannot be added. Non-local users cannot be given rights on this server

The user 'insert user here' cannot be added. Non-local users cannot be given rights on this server

If you get the above error when trying to add a user as a delegate in Outlook, it's because the user mailbox is a Shared mailbox. You can easily remedy this by going to EMS and typing:

Set-Mailbox "mailbox user or alias name" -Type Regular