When receiving email from groups, sometimes items arrive from a group not subscribed to. How can one figure out how it was routed?
Look at the email headers, e.g. with Gmail's Show Original menu action.
Search in that text for the following items to see intermediate groups that were part of the routing path:
- for <
- Part of the Received: fields, which show groups and individuals a message was received for.
- Shows email groups that have received a message. The mailing lists add this to avoid loops, ignoring an incoming message already marked by the same group.