annasassy86,
In Oultook Web Access there is an option on whether to show or hide messages that are pending deletion.
Pending deletion sometimes referred to as marked to be deleted, or marked as deleted is part of the IMAP protocol, as well as implemented in Exchange's own protocol.
IMAP was designed for multiple devices or location to be accessing the same email account. The potential to delete something important and later need it at a different location was recognized. Messages are marked to be deleted. Different mail clients handle it in different ways. The iPhone does not show messages that are marked to be deleted. Outlook, Outlook Web Access, and Entourage show them be default either greyed out or with a line through them. Mail.app is OS X doesn't show them by default, but can be told to show them as discussed in this article on recovering a message that has been accidentally deleted:
http://docs.info.apple.com/article.html?path=Mail/3.0/en/9911.html
Hope this helps,
Nathan C.