Notification behaviour (to/cc) - please only notify upon "to"
Currently a user is notified whenever the user's url is part of the "to" or "cc" header of a message. It would be great if that behaviour could be changed so that only a "to" would cause a notification, while a "cc" just is some "this mail is also for you". I think this reflects the workflow how people do work with mails. When I get a (business) mail where I'm in the "to" header, then I will (mostly) read it. When I'm just mentioned in the "cc" this is a sign for me, to read the mail, if I have the time to - and it wouldn't be a problem, when I wouldn't read it at all.
But there is another - more important point: When commenting a post, the receivers in "to" and "cc" should always be copied into the comment, so that the post will reach all intended persons. This isn't possible, when the receivers had been added in "bcc/bto", since this data field must never leave the sending server, see the discussion here: https://github.com/w3c/activitypub/issues/326