The LAMMPS mailing list was hosted since 2005 at SourceForge and was discontinued on June 30th 2022.
In 2021, LAMMPS joined the Materials Science Community Discourse website as a forum for discussions about LAMMPS.
See forum details here. This is now the main place for communication of the LAMMPS user and developer community. The forum also contains an archive of all past mailing list messages.