The requirement is to create and maintain an understandable record documenting activities. Some replies to e-mail messages contain enough information from the original message that they can stand on their own, but most do not. The simplest way to ensure understandability of e-mail messages that will become part of the record is to incorporate the original message in any reply and maintain them as a unit. Retain e-mail records in accordance with your office's file plan and the DOI records disposition schedules. The exact length of time will vary depending on the activity that the message documents.
Retentions range from thirty days to thirty years.
Delete e-mail that is not a record when no longer of use. You should store e-mail records in an approved recordkeeping system. This system may be either paper or electronic. First of all, not all of your e-mail messages will be records. Second, if your organization has an electronic system to manage messages that qualify as records, the records should be maintained in that system.