When posting to the mailing lists, please keep the following in mind, as they will increase the likelihood of getting a useful response:
The valgrind-announce list is a very low-volume list for announcements of new Valgrind releases.
The valgrind-users list is a general discussion list for anything that comes up when using Valgrind -- if you can't work out how to use it, if you don't understand an error message, you have an idea for a new Valgrind tool and want some feedback, etc. It is read by all the developers, plus a bunch of other knowledgeable folk. Unfortunately, as with any mailing list, there's no guarantee that your question will be answered. The list is archived at Sourceforge.
The valgrind-developers list is aimed at developers. It is for discussion of technical implementation details, and is where developers meet and discuss issues, code changes, etc. The list is archived at Sourceforge.
The results of the nightly regression tests are sent to the valgrind-testresults list. This list is archived at Sourceforge.
There is an IRC channel for Valgrind developers: #valgrind-dev at irc.libera.chat. See Libera.Chat for how to connect your irc client.