1. The envelopes, probably not. They would probably at least keep a log of correspondence received and sent, accounts payable and receivable, payment receipts, etc. If they have stories that make factual claims then they'd want to retain the journal/notes that went into each story for some nominal amount of time as well, if only to defend their name later.
2. Don't know, but the easy answer is "As long as the government required it to be". Even the NSA gets rids of their data after 5 years (or so they say).