Email Archiving Retention Standards

Hello All – I have been given the task of researching and creating our email archiving retention policies (as well as creating our records retension policies) in preparation of our SAN deployment in the coming months. We are a Engineering and Environment firm here and California an work closely with state and local agencies, so I am assuming that we would have to retain the same policies/regulations that the State must follow. With all the data and info out there, I’ve become overwhelmed with the task. Has anyone out there dealt with this project before and can give examples of their retention policies? If not, can you point me in the right direction? Thank you in advance as it is much appreciated!!!