There are plenty of reasons why you might want to give one user access to another user's mailbox. The first user may be in the hospital, or under HR review, or maybe they've been dropping the ball lately and management need to make sure that certain projects have been followed up on. It's not really our job to care. The fact is, Bill in management has requested that you give Paul Stanley access to Gene Simmon's mailbox, and for various reasons, logging on to Gene's mailbox to set these permissions up is not a good option. For one, you'd only be able to delegate access to certain primary folders, not to the whole mailbox, and second, you'd have to know Gene's password to do that. Because you are a smart admin, you tell Bill you can take care of it easily from the server.

Giving one user access to another's mailbox via PowerShell