There are two mailing lists for LibreSSL:
libressl@openbsd.org — public list for technical discussion about LibreSSL on any operating system.
libressl-security@openbsd.org — private list for reporting severe vulnerabilities in OpenSSL or LibreSSL to the core LibreSSL team.
See https://www.openbsd.org/mail.html for more details on posting or subscribing.