Yes, I'm saying neither chat nor email solve this issue.
Email is far worse, in fact, because:
* Everyone has a unique view
* Unless there are lots of cc-everyone style emails, you might not even have anything to find. (And cc-everyone sucks for 100 other reasons.)
* You can't find anything predating the start of your employment
The biggest issue with searching both chat and email is the absence of a result doesn't help: it's possible it was a private chat, or an email chain that you weren't a part of, but there's no way to tell.
(Side note: A very locked-down wiki isn't any better, but that's a conscious decision rather than default.)
Mailing lists are not heavily used outside of free software. In the corporate world I’ve never had a project provide a mailing list to be used for discussions.
