Brad Knowles writes:
How does it break mailing-lists? If the list sets the envelope sender
to <firstname.lastname@example.org> creating a MAIL-FROM shouldn't
be a problem.
You may be surprised to discover this, but most mailing lists are not proper mailing lists and are not managed with proper mailing list management software. Most mailing lists are actually handled as aliases, and therefore do not modify the envelope sender address.
The only problem I can see is what to do about bounces
(i.e. with a null envelope sender) - guess you could use header From
Actually, this is one area that the paper addresses.
That's a new requirement in a new RFC. How many sites are there in the world that run older MTAs that do not necessarily always implement this rule? Indeed, are there any MTAs which exist today that enforce this rule in all cases? Even if you do have an MTA which implements this rule, what if all you have is the alias, and there is no "-owner" or "owner-" address defined?
So, you run a big site, with tens of millions of customers. Are you going to tell them all to "piss off" if they're subscribed to a mailing list that is not implemented according to this rule?