New Mailing List Access Level List of Permitted Senders
Change the access level of a mailing list not only to be limited to "members", "everyone", and "read-only" to also include an option for allowing a list of addresses for a particular list or domain. Updating the list of permitted Addresses should have a similar API access as editing mailing lists. This allows specific people to send to lists they are not on, but also restricts unwanted senders.
Mailing lists are too limited currently in my opinion. We should be able to define inbound rules/filters on for sending to the list. The best would be to allow the same kind of regex on any header as conditions, the same way it's used in custom routes, e.g.: