On Thunderbird, I create local copies (select all messages, right-click, copy-to local folder), right-click on that to properties, find its location on disk, an

On Thunderbird, I create local copies (select all messages, right-click, copy-to local folder), right-click on that to properties, find its location on disk, and compress and archive. Not sure about whole portability aspect of this, recently upgraded my desktop and copied straight from one Thunderbird local directory to the other, that worked. But I wonder if Thunderbird upgrades, if there'd ever be a problem with this method.