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Reply-to munging is a technique used by MailingLists: they munge the Reply-to: field in the message header to point back to the list software (eg "foobar-discuss@foobar.com") instead of the individual who posted to the list.

Reply-to munging considered harmful?

Some UNIXites have complained heavily that modern mailing lists munge the Reply-to: field in the message header to point back to the list software. Mailing lists do this so that replies automatically get sent to the list software. However, sometimes this creates problems, because a Reply-to: header changes the default understanding that one replies to the author of an email. Consequently, occasionally someone will end up sending libelous material to a list thinking she had replied privately.

The argument against reply-to munging essentially suggest that subscribers use the reply-to-group functionality in their mailer, even though most users don't know it exists, and for those that do, replying-to-group is unnatural. The essay suggests unhelpfully that

Whichever mailer you choose, please read the fine manual that comes with it.

However, the real problem is that the reply-to-group function is even less correct than normal "reply". Not only will the reply-to-group send a copy of your message to the list, but to the original author as well. This means the original author receives two copies. Things get worse in a long message thread as the To: field grows with each reply, snowballing the mailing list. This is just plain aggravating. To get around it, as a conscientious user, one has to edit the message header in every case instead of only exceptionally in exceptional cases. This is not a HumaneInterface, and so people don't do it.

Really, the essay is just another bastion of the great UNIX user interface design philosophy:

In an ideal world, all our users would be scriptable.

["Reply-To" Munging Considered Useful]

If you are trapped on a list whose administrator is insane, you might want to consider this strategy if you're willing to ruffle a few feathers. Create a Yahoo! group or some other mailing list that has the correct behaviour. Subscribe the Yahoo! group to the insane list (!!). Unsubscribe yourself from the insane list. Read and reply to the Yahoo! group.

The IETF weighs in

In [RFC 2282], the IETF finally clarified what's supposed to be done with the Reply-To field: the list is not supposed to munge it.

When the "Reply-To:" field is present, it indicates the mailbox(es) to which the author of the message suggests that replies be sent.

The list software is not the author of the message, in any sense. It isn't even the editor. It's the publisher.

["Reply-To" Munging Still Considered Harmful. Really.] has more information on this.

The Two Laws of Reply-to Munging

  1. If there's a broad consensus of your users about reply-to munging, do it. RFC 822 sec. 4.4.3 says it's OK, but it's not mandatory either.
  2. On software-related lists, there will be a consensus in favour of leaving reply-to as poster. On all other lists, there will be a consensus in favour of setting reply-to to the list, even after embarrassing accidental posts.


I don't think a generalization and assumption such as this second "law" can be considered a law. I'm on several software-related lists. All use ReplyToMunging. -- EarleMartin

I find people who are religious about this to be really frustrating. All one has to do is look at the actual observable behaviour as a result of doing it the 'proper' way to see how incredibly dysfunctional that approach is, even if it is ideologically correct. It was worth trying, but decades of history have proven it doesn't work, and so one should munge the reply-to. -- SunirShah

It should be noted that many mail clients also have an option to ignore the reply-to header or ask whether to use the reply-to or From before sending the message. -- Anon.

I've moved this to a page of itself, it's an important enough topic. see also http://css-discuss.incutio.com/?page=CssDiscussListHeaders -- I'll probably take stuff from that page & bring it here, since it's off-topic there)


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