People interested in ns-3 development should subscribe to and read the ns-developers mailing list, a Google Group since November 2022: Google Groups page  Archives prior to November 2022

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

A few additional developer-oriented lists predate our use of GitLab notifications, but the archives may still be useful:

• ns-3-reviews: ns-3 code reviews. 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. Archives
• ns-bugs: Automatic mail from Bugzilla database updates. Archives