Most Thunderbird / desktop tag implementations are done by just copying the message to multiple folders (which achieves nearly identical behavior, which is grea

Most Thunderbird / desktop tag implementations are done by just copying the message to multiple folders (which achieves nearly identical behavior, which is great. It's just not usually optimized UX). And most servers don't deduplicate messages globally (I'm not sure why, tbh. probably there's some rational-but-depressing reason).