Someone is illegally accessing my e-mail account



Windows XP and my e-mail client is Outlook Exress6.
Share my computer with others, but all have their own e-mail account and
password.
Very strong suspicion that someone is reading my mail.
Can I access a log of when my account has been accessed? If so, where is it
and how do I do it. This would tell me the occurrences of when it's not me.
Obviously will change my password, but would like to track down the culprit!
--
Gunter
.