To me, that looks like a fundamental issue.
Some benign Messages and Records are normal to end up in the Trash Bin.
Others, however, Players might want to conserve without time limit.
That's where the ages old Idea of the "Persistent Personal Data Log" comes in : the Player building up a personal "Encyclopedia Galactica" based on Data gathered off many different Sources.
After discovery, all available for later review at anytime.
In my book, such Audio logfiles from the Generation Ships would be part of such a permanent Database of Information the Player should build up over time.
The old Problem : the total lack of Information handling, accumulation, exchange and -brokering in ELITE on an individual per-Player basis...
So be it Data gathered off Beacons, Data Links, Compromised Carrier Messages, Scans, Logs... The Message Inbox just isn't made for a sorted and permanent Storage.