I use non-outlook (pop3) mail accounts e.g. arie@schaberg.nl. Messages older than a month are moved from my computer and must be found using 'search'. There, just a few older mails are found (about 2 months older). Older yet mails must be found using 'online search' (I use no online storage like a cloud). There older mails (e.g. august 2017) are found. But I cannot move them to my computer. And Mail shuts itself down after 30 seconds.
This really needs improvement.