Adding Gray Duck Mail to Communication - Email - Mailing Lists and Newsletters (#2975)

fixes #2975

README.md

@@ -424,6 +424,7 @@ MTAs / SMTP servers
 Mailing lists servers and mass mailing software - one message to many recipients.
 
 - [Dada Mail](https://dadamailproject.com/) - Web-based list management system that can be used for announcement lists and/or discussion lists. ([Source Code](https://github.com/justingit/dada-mail)) `GPL-2.0` `Perl`
+- [Gray Duck Mail](https://grayduckmail.com) - Self hosted email discussion list management that uses external email providers. ([Source Code](https://github.com/wagesj45/gray-duck-mail)) `GPL-3.0` `Docker`
 - [HyperKitty](https://wiki.list.org/HyperKitty) - Open source Django application to provide a web interface to access GNU Mailman v3 archives. ([Demo](https://lists.mailman3.org/), [Source Code](https://gitlab.com/mailman/hyperkitty)) `GPL-3.0` `Python`
 - [Keila](https://www.keila.io) - Self-hosted reliable and easy-to-use newsletter tool. Alternative to proprietary services like Mailchimp or Sendinblue. ([Demo](https://app.keila.io), [Source Code](https://github.com/pentacent/keila)) `AGPL-3.0` `Elixir`
 - [Listmonk](https://listmonk.app/) - High performance, self-hosted newsletter and mailing list manager with a modern dashboard. ([Source Code](https://github.com/knadh/listmonk)) `AGPL-3.0` `Go`