For example some of these email stores like the usual Outlook PST requires Outlook to read and use what's in the PST file. There is no loss of information when we copy this file to backups but to restore access we have to put it where Outlook expected it.
Similar rules for other mail apps.
Over the years and on several e-mail accounts (Prodigy, AT&T, Yahoo! & gmail), I've accumulated a huge number of emails with family history information that I'd like to save onto some external media (disks, cloud etc.) to guard against losing that information should any of those email systems suddenly disappear (as happened years ago, of course, with the venerable but ancient Prodigy).
I know that I could now access each message and copy/paste then individually or such ... but that would take forever and would likely be subject to various errors (due to user fatigue, boredom etc.).
Is there any way to copy email messages wholesale -- say a folder at a time -- to external media that would retain all the messages' information (including links) so that content could be accessed/read at a later time, even if the original email system is no longer operational?
I look forward to your detailed instructions and pointers.