Users with the tag: custom mailing lists
None! It looks like no users are currently using this tag - at least not publicly. Since the tag exists that means there are profiles using it, but they've marked their profiles private. You can always see other tags in active use when you browse the public profiles created by members of our community.
But since it looks like No Users are currently tagged with custom mailing lists publicly, why not create a profile on KnowEm and become the first?