GNU Mailman is a free, open-source mailing list management platform for organizations and communities that use email for discussions and newsletters. Written in Python and distributed under the GNU General Public License, it combines email-based list services with web tools that make it easier for subscribers to manage their accounts and administrators to oversee lists.

Mailman offers features including built-in message archiving, automatic handling of bounced mail, content filtering, digest delivery, and spam filters. The project provides two major versions: Mailman 3, comprising components such as Mailman Core, Postorius, Mailman Client, and HyperKitty, and the established Mailman 2.1 series. Users and administrators can access documentation, FAQs, security information, source code, and community support resources. The project also welcomes contributions and donations, and connects users with developers and the GNU Mailman Steering Committee through email and IRC. Developed by an international community of contributors, GNU Mailman supports the practical work of running and participating in email lists, from everyday subscription management to list administration and archived discussions.