The Problem when using tags like folders:
Solution to find ALL tagged emails - and to get a completely reliable situation with masses of tagged emails:
Some details:
To really use tags as a replacement like folders, - it is important to see (to get feedback), - if ANY TAGGGED email doesnt match to the ACTUAL visible tag-entrys (- the list from tag-menu). - "Show others" in a menu would give feedback, if all tagged email is adressed reliable with the actual tag-list.
In everyday-usage a simple renaming of a tag, or deleting and adding of a tag ... - could result to overseen problems (tag-keyword (in prefs.js) will be different, while the visible tag-name in menu is OK).
-> A simple "show others" in a menu (within the tags-menu) can give the right feedback to the user - to solve all possible mistakes with tags (renaming a tag or its keword (prefs.js ...)). - So one can say "use your tags as folders !". (Scanning Email for tags is done anyway ...)
(With such a simple feedback to the user, thunderbird TAGS are perfect (with IMAP and workgroup/network with postfix-server))