Mailbox cleanup agent - message date query

[DRitchie]

I have a query regarding the message date that the mailbox cleanup agent uses when selecting messages to delete. Does the agent look inside the message file to get the date the message was received (or sent in the case of sent messages) or does it use the windows MAI file date stamp? In my case for one mailbox there are many MAI files dated 30/04/2014 when I view them using Windows explorer, but when I open the files in notepad the dates received are different (and are prior to 30/04/2014).