Confusion between Reply To and Reply List in email responses

So this is something they are doing manually, by typing or pasting it in themselves? That’s… quite odd.


A badly behaved mailing list would have the reply to set to the list address, and a user who wanted instead to reply to the sender could change the address to the sender address, which was the address of the person who sent the message. I guess that behavior is so strong that people would not look at the address to see that it couldn’t possibly be that of the person who wrote the message.

For one mail-centric community I wrote a plugin that reveals the email address of the poster to make it possible to reply directly to the sender via email.


Do you have any details about how people are doing this? Is their email client giving them the option to use the From address, or are they manually copying it into a new email?


One data point, since I have seen this issue:

In Thunderbird (I’m running v78.7), I believe that it recognizes Discourse emails as coming from a mailing list and offers two reply buttons – Reply and Reply List.

Reply will create a reply going back to the “From” address (

Reply List will create a reply going back to the “Reply To” address (

I personally find it very easy to accidently hit the reply button instead of the reply list button.


Hi all —

Thanks for the responses on this thread, and particularly to @simon for the notes about customizing the email responses. I will look into that more.

To @codinghorror and @simon 's questions:

I know that some of our team members who ran into this use Thunderbird, so were likely running into the behavior @Beakerton notes (and I know some old-school UNIX-based mailers do the same thing; I hadn’t actually realized that Outlook doesn’t make it easy to do so until writing this response). If it’s of interest, I can ask the other users whose mailers I’m uncertain of how they ran into this, though I expect it’s similar.

To @pfaffman’s point:

I think that could be the case. Or that if they are thinking about it, they may believe that something “magical” in Discourse is anonymizing the sender’s address but will make sure their response reaches them? (I realize that this isn’t the case, and understand the reasons why so am not suggesting I believe this should occur).

I think an advantage of customizing the “From:” address to something that looks less like a reasonable address as @simon notes here:

would dispel those illusions for those paying attention, or possibly just make it less surprising that things didn’t work if they go back and look at their sent message. But being able to customize the “bad destination address” message would probably get us 95% of the way there, so I will look into that more.

Thanks again,


I still have the From: header as and was thinking of making it something more welcoming (partly in case people didn’t think replying would work). Noreply must either be a default or recommended setting.

But maybe the answer to both problems is in the first part of this sentence:


Our experience is that this indeed happens to Thunderbird users.
Nowadays it’s the first question I ask when someone reports an incident like this, and the answer is always ‘yes’.


Definitely a Thunderbird thing as we discovered and tested around mid January:

Reply - one message - goes to [](

Reply-All - two messages - goes to both [](
and [](

Reply-to-List - one message - goes to

Turns out there is even an add-on for Thunderbird to fix this:


Yeah I strongly view this as a design error in Thunderbird.

However I sympathize with your users who are simply trying to do the right thing. I think about the best you can do at the moment is to customize the error message so that it is specific to your community and puts the most common error remedy at the top of the response, something like:

We’re sorry, but your email message to ["[project]"] (titled Re: [Subject]) didn’t work.

If you are using Thunderbird as your email client, you must reply to the list; it is not possible to reply directly to users via email.

Do you use more than one email address? Did you reply from a different email address? Email replies require that you use the same email address when replying. Alternately, the Message-ID header in the email may have been modified.

Not that exact text, of course – whatever you think makes sense, listed near the top.


I’ve updated our error message thanks to the tips in @simon’s message above and suspect that this will be sufficient to address the confusion that some in our community have felt. If there were a way to customize the “From:” address to something more like that would be icing on the cake, but for now I think we’re in a much better place.

Thanks again for all the help here,

PS — As long as we’re bagging on Thunderbird in this thread, I’ll mention that it’s still perplexing to our Thunderbird users that URLs from their HTML-formatted messages seem to get dropped on the floor by Discourse’s incoming mail processing filter, where it remains unclear to me whether this indicates a Thunderbird bug or a Discourse bug.


Based on this feedback, we’re also going to improve the error message in general. It will look like this in current beta and future releases:

We're sorry, but your email message to %{destination} (titled %{former_title}) didn't work.

Here are some things to check:

  - Do you use more than one email address? Did you reply from a different email address than the one you originally used? Email replies require that you use the same email address when replying.

  - Did your email software properly use the Reply-To: email address when replying? Unfortunately, some email software incorrectly sends replies to the From: address, which won’t work.

  - Was the Message-ID header in the email modified? The Message-ID must be consistent and unchanged.

Need more help? Reach out to us via the Contact Us details at  %{base_url}/about

But I can open my old discourse messages in Thunderbird without this problem. Only newer ones has this problem. I’ve described it in my post:


I guess you’re right and the presence of the List-Post header understandably makes Thunderbird think it’s a mailing list email. Probably a Reply-To header would suffice.

The following is from RFC 2369 - The Use of URLs as Meta-Syntax for Core Mail List Commands and their Transport through Message Header Fields

3.4. List-Post

The List-Post field describes the method for posting to the list. This is typically the address of the list, but MAY be a moderator, or potentially some other form of submission. For the special case of a list that does not allow posting (e.g., an announcements list), the List-Post field may contain the special value “NO”.


List-Post: (Postings are Moderated)
List-Post: NO (posting not allowed on this list)

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We don’t expose email addresses as that would be a privacy violation.

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I’m not an email expert so maybe wasn’t clear.

It seems that the emails have and - I’m only basing this on this topic, not from having checked, so could well be wrong.

I wondered whether and would work without confusing Thunderbird.

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The email notification headers we’re providing are correct. The mismatch comes from the user’s mental model of what is happening …

this user David is emailing me directly

… versus what is actually happening.

the forum is notifying me of activity on a topic

My hope is that the improved email error message will help teach the user the difference. It is a challenge to move email-only users to a hybrid web forum solution. :e-mail:


I understand that difference, but if you’re using Reply-To why also use List-Post?

I’m not saying it’s wrong - I just wonder. Purely based on this topic it seems to confuse Thunderbird and (if Reply-To works) to be unnecessary.

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IIRC, adding the header made some different mail software behave correctly. The history should be on Meta somewhere.


I’ve had a quick look. It seems that this is the genesis of the List-Post header: Emails are not threaded in Outlook 2013 - #5 by codinghorror

I’m not sure that it was fully thought through or that it was relevant to the problem being solved there (but again I’m still learning here myself).


Looks correct to me. What’s incorrect is mail software that ignores the Reply-To address … it’d be like you introducing yourself to me as Jonathan, but no, I insist on calling you Edward instead. :wink: