Musl has a single mailing list for development discussion and user support. Questions and comments related to compiling musl, compiling software against musl, porting, bugs, differences between musl and glibc or other libc implementations, feature requests, etc. are all on-topic and welcome.
To subscribe, send a blank message to musl-subscribe ΑT lists.openwall.com, then reply to the confirmation message you receive. You can also mail the list without subscribing by sending email to musl ΑT lists.openwall.com, but messages from non-members may be held for moderator approval. If you are not subscribed and want to receive a reply, please mention in your email that you want to be Cc'd.
Mailing list archives are now online.
Most development discussion and discussion with integrators working to build self-hosted musl systems take place on the #musl channel on the Freenode IRC network. Users are also welcome to seek support here.