People interested in ns-3 development should subscribe to and read the ns-developers mailing list: Join  Archives

A few additional developer-oriented lists are still in some use but are gradually being phased out in favor of using GitLab notifications:

• ns-3-reviews: ns-3 code reviews. Join/Archives
• ns-commits: every Mercurial commit pushed to one of the repositories hosted on code.nsnam.org generates an email describing the commit, and nightly validation messages. Join  Archives
• ns-bugs: Automatic mail from Bugzilla database updates. Join  Archives

For user-oriented mail (getting help with using ns-3) there is also the ns-3-users mailing list: Google Groups page