List-Id: A Structured Field and Namespace for the Identification of Mailing Lists
Software that handles electronic mailing list messages (servers and user agents) needs a way to reliably identify messages that belong to a particular mailing list. With the advent of list management headers, it has become even more important to provide a unique identifier for a mailing list regardless of the particular host that serves as the list processor at any given time. [STANDARDS-TRACK]