Same newsletter create multiple feeds

@samuelclay I just wanted to pop by and say, thanks. I think this change resolved a long standing issue I had where all newsletter emails from a large org (e.g. nytdirect@nytimes.com) were all routed to the same feed even if a different list-id. The behavior I’m seeing now changed not only to merge emails from different senders with the same list-id but also to split emails from the same sender with different list-id. Thank you!