[yam] Resent-From and Mailing Lists

Sabahattin Gucukoglu <mail@sabahattin-gucukoglu.com> Tue, 13 April 2010 12:06 UTC

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Date: Tue, 13 Apr 2010 13:06:03 +0100
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From: Sabahattin Gucukoglu <mail@sabahattin-gucukoglu.com>
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Subject: [yam] Resent-From and Mailing Lists
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Hi all,

I am puzzled.  I contacted the mlmmj (a mailing list manager) mailing list, with a query about mails being rejected on mlmmj-run mailing lists when resent.  The mailing list manager would reject mail, sending the rejection notice to the From: person, because the subscriber resending the message was in the subscriber list but the From: person was not, and because the From: person was the one being checked.  The effect is that the originator, not the subscriber, gets a notice and the mail goes nowhere, even though the Resent-From header would have authenticated the subscriber to the mailing list, allowing him to mail to the membership a message coming from the originator, just as Resent-* headers are supposed to.

The maintainer quotes this passage from RFC 5322 as justification for this behaviour:

   Resent fields are strictly informational.  They MUST NOT be used in the normal
   processing of replies or other such automatic actions on messages.
...
      Note: When replying to a resent message, replies behave just as
      they would with any other message, using the original "From:",
      "Reply-To:", "Message-ID:", and other fields.  The resent fields
      are only informational and MUST NOT be used in the normal
      processing of replies.

So, it seems there is some connection with automatic action being unsupportable specifically because the Resent-* fields are given this prohibition, rather than the From:, even though neither is really correct because neither is suitable for automatic replies, while the check against the Resent-* fields clearly does not mean that a rejection message should be mailed there.  The envelope is clearly the right place to find the sender address for rejections (loops and all that), although I know that for example Mailman does not use it but instead the Reply-To/From if it cannot identify the subscriber.  In any event, what this means is that, assuming the usual automatic responses being mailed using Reply-To/From, any mail sent as a result of resending needs special treatment in certain circumstances, like this one, which appear to violate RFC 5322, .  The only way this makes sense is for Resent-From: to receive any automatic replies, and that is clearly wrong, while the originator is clearly also not required to be a member of a mailing list for Resent to be, at least semantically, supportable.

To be clear, is there anything wrong with "Authenticating" against Resent-From, as one might "Authenticate" against From?  This mailing list manager at least does not support post acknowledgements, so there would be no need to reply if the subscriber could be verified.

I understand absolutely the intent of the paragraph that states replies go to the originator, but what does this say for automatic responders more appropriate for the sender and not the originator?  Is this the vacation quandary all over again?  Or have I simply misused the resend function, that of allowing my mailing list participants to see a message as sent to me, often from another mailing list?

Cheers,
Sabahattin