grombleton on "[Plugin: Contact Form 7] Exchange Server Rejecting Emails"

My client is using CF7 - their emails go through a Microsoft Exchange Server before hitting their inbox - they don't seem to get any of the emails when a client submits the form.
I've tried using 3 other email accounts (all POP/IMAP) and these collect the emails ok - is there an issue with CF7 and Exchange servers? If not, would you have an idea on what is causing this?

http://wordpress.org/plugins/contact-form-7/