Here's the scenario:

A person from Company A sends an email to two people ( X and Y) in company B and CCs a person in company C.

X replies using 'reply all' but deletes the company C CCed recipient.

The email, when viewed in X's 'sent items' shows the correct recipients but when viewed in person Y's inbox shows the CCed part that was removed.

The email did actually go to the removed CCed party.

The closest we can get to replicating this is by adding a Rule which on outgoing messages CCs a third party and while the CC does not show when the sender composes the message, it does show when he looks at it in his 'sent items' - so this is not it.

Any ideas?