From my understanding, you would like to retain a history of last accessed by field in ESM. This is a MAPI property and must be scripted out. There is no easy way to perform a constant recording of whos logged in. The closest is a script written by good friend and Exchange MVP Glen Scales who a great script to script this information out. However, since you’re wanting to record and retain a history, you would have to run these scripts periodically. Another method is to run Exchange Exmon utility which does a constant capture. There is also a limit (512KB I believe) in one capture before starting a new capture. This however, only logs IP addressed of computers that have accessed the mailbox. I hope this helps, if anything is unclear please ask.
Displaying the Logon Status using Data shaping via ADSI and the Exchange_Logon WMI Class in Exchange 2003
MCSE | M+, S+, MCTS, Security+