maybe it's time to remove those links.
Agreed, but I simply don't have the time to go chasing them down. The site is a WiKi, so anyone who has asked for, and been granted, appropriate access rights could do it, to help out.
maybe it would be nice to provide some info about how to search through those mailing lists
Indeed. I tried a site specific Google search, but it doesn't seem to be able to access mail-list archives; may be worth asking OSDN.net's own tech support.
The mailing lists page http://www.mingw.org/lists.shtml refers to http://gmane.org . Sadly, gmane is dead for a few years already (see https://news.ycombinator.com/item?id=12180547 ). So, maybe it's time to remove those links.
Also, maybe it would be nice to provide some info about how to search through those mailing lists. Cause the only archive I see ( https://osdn.net/projects/mingw/lists/archive/users/ ) does not offer any convenient search functionality, as far as I see.