DM/PM Exchange Recovery

Bit of an odd one/only applies to this certain scenario you might have gotten yourself into. But, having the ability to reopen the DM exchange between you and another person that you are neither friends with anymore or in a server in. As of right now, you cannot search up that DM exchange if you are no longer in a mutual server as well as no longer friends, and therefore it practically just disappears;lost to the sands of time... Essentially just being able to locate any DM history with anyone that you have ever had an exchange with in a DM before on that account. Although I'm assuming for capacity purposes it would have to limited to either a certain time allotment (I.e. only exchanges from the past year or so, give or take) or count towards one of the number of maximum DM's that one has "opened" (although it would technically be closed). If it were to be the latter as opposed to the former. Than I believe there should also be a means to essentially clear a "cache" of stored former DM's, as to then not take up any unneeded capacity; and so a user could go and clear whichever ones they know they would no longer want to keep/need ever again. Again, it's a bit out there, but I appreciate any and all feedback on this bit of a unique solution to an obscure predicament. Thank you for your time.