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

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

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