with your companies legal department. The bank where I consult does backup all of it's e-mail but only for use if some form of law suit is brought against them for somethig=ng that one of their workers has sent out as it is possible to alter an e-mail and then forward it on to a third party with unknown conquences. So they backup everything just in case something like this happens.
However this is a new pratice as recently they had a suit brought against them by someone who was refused credit and somehow an e-mail was leaked to this person who's contents where like nothing that was in the original it was actually quite deflametary in fact and if we could not prove that the recieved e-mail to the third party was not exactly what we sent there would have been a horendious payout involved.
Most people don't realise that e-mail is the same as letter writting so I advise all my clients never to put in an e-mail what they would not be prepared to comit to paper and always backup any sent e-mails just in case someone alters the original so at least you have some proof that what gets recieved by some third party was not what was sent originally. But this is a legal minefiels and it is up to each indivual company as to what they want to do in this area.
Because this is a bank involved we get some leniency from the courts just so no one can go on a fishing trip and gather something totally unrelated we can provide the required files to the court for them to read and then forward on any that are pertant to the case in question but general business doen't have this luxery so it is one for the legal department to answer.