I am moving some of my mailing list inboxes from a private system to Gmail where I want the list messages to go into separate "list inbox" folders, rather than the main inbox. I started by bouncing a list message from the other system to Gmail and, when I went to set up a filter for the bounced message, Gmail seemed to recognise that this was a message to a list and suggested a filter in the "Has the words" field of list:(x.x.jp). (The list sends messages to x@x.jp; I've changed the name of the list itself here to x.)
What exactly does this match in messages? My instinct would have been to put x@x.jp email address in the "To" line of the form (where I presume it would match against both the To: and Cc: headers).
(Edit: The rule from the match suggested to me seems to exhibiting some odd behaviour as well; the action is Skip Inbox, Apply label "__Inboxes/x", and no other rules apply that label, yet some of the messages I've bounced since have both Inbox and __Inboxes/x labels.)
The only place I've seen this mentioned in previous questions is in Filtering Apache mailing list emails in Gmail, which makes it clear that the feature is at least ten years old, but does not explain how it works. The answer to that question also uses x@x.jp syntax rather than the x.x.jp syntax that was suggested to me by Google.
Other questions that address mailing list detection in Gmail but don't mention list: at all are 2962, 17271 and 28159.
