That article is out of date. When the wiki was locked 2 years ago most KB articles had been updated to support version 60. A lot has changed since then. Our KB articles can still be useful, but in many cases you need some sense of what has changed after version 60 to know when its safe to rely upon them.
There are no copyright issues. The folks supporting
Mozilla's Thunderbird knowledge base (frequently called SUMO due to SUpport MOzilla .org) ported our Thunderbird KB articles long ago and modified them to meet their guidelines. They are reasonably up-to-date but they have limited resources. They prefer short non-technical articles so some KB articles such as the one you ask about were not ported. They also require editorial approval so they always follow the "party line". Sometimes this means a change that Thunderbird inherited due to a change in Gecko to meet the Firefox developers needs is touted as a good thing even though its detrimental to most Thunderbird users.
This difference in approach is why I've been occasionally working on porting and updating some of our Thunderbird KB articles to a replacement wiki hosted by Miraheze. I don't want to unnecessarily duplicate what they have, but they're targeting ordinary users (trying to provide the equivalent of a user manual via KB articles) while we're targeting more technical users plus trying to provide technical information not readily available elsewhere that is useful for tougher problems.
Its not ready yet. I keep running into family problems that take priority. When it is ready I'll announce it. It won't effect the links to the KB in the side panel though. We don't know what we're going to do about the existing MozillaZine KB wiki, that will get driven by whatever the long term solution is to keep this web site up and running.
