Re: what should happen when mda sees multiple List-ID headers?

[ebiederm@xmission.com (Eric W. Biederman)]

Eric Wong <e@80x24.org> writes:

> Given my recent traumatic experience[*] around multiple
> From/To/Cc/Subject headers; I guess we should prepare for the
> possibility of multiple List-ID headers showing up in -mda.
>
> Right now, we handle the first one (and I'm updating -learn to
> support List-ID, too); but it's possible that multiple List-ID
> header can map to different inboxes, too...

So I looked at RFC2919 and it had something interesting to say.

- That when you receive a message from a mailing list only the
  List-ID set by the mailling list software should be present.

I think in practice that means if everything is RFC conformant
and working correctly you should never see a message with
multiple List-IDs.

Which leads us to what should we do with potentially buggy software.

Or possibly a creative list processor that realizes that handles
multiple lists, sees that a message is cross-posted and sends
out a single copy of it to the addresses that are subscribed to
both lists.



There are two reasonable things that can be done, and I suggest
we do them both.
- Print a warning. (To be deleted if this case turns out to be common).
- Deliver to all of the lists you have mailboxes for the List-IDs.

I think that would be the most robust response long term, and it
is roughly what my code in import_imap_mailbox so I don't see it
causing any problems at present.

In particular the delivery logic I have been running with for a long
time now is:

		my @dests = email_dest($config, $mime);
		for my $ibx (@dests) {
                	my $im = PublicInbox::InboxWritable->new($ibx);
                        die "no im" unless defined($im);
			$im->add($mime);
		}

So I can say at worst it is harmless to have code that handles multiple
List-ID headers.

Eric