Sorry but there are no native tools which in Exchange or Outlook which gives this information. There may be third party tools, but I do not know them. Perhaps someone else does?

————————————-

For Exchange, open the Exchange System Manager. Go to Administrative groups -> Servers -> Your Server -> Mailboxes. You can see the last time a user logged into a mailbox.

**********
Mshen, that shows who last logged into that mailbox, yes, but the question was how to get a historic log of those who accessed the mailbox. The suggestion you gave does not give the HISTORY of logins; it only shows who is currently logged in or who last logged in. Also if someone is just viewing the free/busy time of another user they will show up there as being “logged into” that mailbox even though they are not.