Btrfs mailing list
The Btrfs mailing list is hosted on vger.kernel.org. The email address is firstname.lastname@example.org. You can find details on how to subscribe here (subscription is not required to send mail):
Mailing list archives are available from gmane:
The mailing list server utilizes greylisting (i.e. the server may delay mails) and discards emails that are in HTML format or that exceed 100,000 bytes. And please disable word wrapping in the mail client for sent mails that include kernel log backtraces.
The old mailing lists on oss.oracle.com are no longer active, but the gmane archives do include the old list as well.