Tagging mailing list
Tagging mailing list is one of the most active OSM mailing lists.
It is for tag discussion, strategy and related tools.
Its main page is at lists.openstreetmap.org/listinfo/tagging where one may subscribe or view archives.
Note that it has quite significant activity, it may be useful to create separate mail account just for it. Or setup mail filter putting its messages into a separate folder.
Tagging mailing list is very useful to find problems with some new proposed tagging, for example due to diverse situation across world: many assumptions obvious for someone in one country will be not applying at all elsewhere.
community.openstreetmap.org - https://community.openstreetmap.org/c/general/tagging/70/ tagging discussions on official forum (login with OSM login)