I was having a problem with the GNU Debugger (GDB) and while the issue appears to be recurring, I found only one instance of someone recently experiencing the same problem. I found this other instance on a Mailman archived mailing list.

Then I tried some more things and finally solved the issue with GDB. So, now I want to report back the solution I found to the mailing list. However, this is really only of use if Mailman recognizes my mail as being the same thread as the original problem, but I do not have that mail (just the online archived version of it) so I cannot reply to it.

How can I make sure Mailman considers my mail as a reply to that thread?

Is simply copying the topic enough?


5 Answers 5


For one thing, even if you do reply to that old message, Mailman will still show your email in the month it was sent. So it's probably not worth the hassle to try replying to a message you don't have. Just send a new email out to the mailing list with your solution (assuming it is topically relevant).

However, for educational purposes: copying the subject won't be enough, because not every message on a mailing list can be expected to have a unique subject. The standard way to indicate that you're replying to a message is through the email header In-Reply-To. The value of that header is taken from the Message-ID header of the message you're replying to. Normally this is done automatically by your email client, but if you use a program that allows you to set custom header fields, you should be able to do it manually. If you go to the list archives of the mailing list in question and click on the "Gzip'd text" link for the month in question, you should get a gzipped text file that includes the Message-ID headers for each email sent that month. Copy the value of the header from the message you're trying to reply to, and add a custom In-Reply-To header with that value to the message you're sending. For instance, if you see

Message-ID: [email protected]

in the message you're replying to in the downloaded text file, you should add the custom header

In-Reply-To: [email protected]

to the message you're sending, and your message will then be considered a reply to the old message.

  • I have already found a thread on mingw-users (the list in question) that spans more than a single month, yet is recognized as a single thread in the archives: sourceforge.net/mailarchive/…. This means your first comment seems not of interest for this mailing list.
    – Jasper
    Commented May 18, 2010 at 2:54
  • 1
    The reason that I want to post it as a reply to that thread is because the problem exists only for a very specific subset of the users (mingw users under x64 windows) and because the question is already a top result in google, it would be a pity if the problem without solution came up higher in searches, while the solution was provided right there.
    – Jasper
    Commented May 18, 2010 at 2:55
  • As for your solution, I am using gmail that does not allow me to specify a custom in-reply-to header, but there are ways around that. However, I can't seem to find any message-ID header in the archive (lists-archives.org/mingw-users/…) but it seems that there is no way around that, so I guess there is simply nothing I can do except copying the topic/
    – Jasper
    Commented May 18, 2010 at 2:59
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    ah, see that link would have been useful. I was basing my answer on a standard Mailman installation (e.g. python-list) but Sourceforge's installation of Mailman is heavily customized. I can't find any way to access the Message-ID header either.
    – David Z
    Commented May 18, 2010 at 6:55
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    Just a tip for anyone coming across this: by using the Gmail API explorer you can manually craft your own raw emails, including whatever header you feel like. Write your email, base64url encode it, and add it to the "raw" property in the explorer: developers.google.com/gmail/api/v1/reference/users/messages/…
    – oligofren
    Commented Dec 11, 2015 at 10:34

According to http://lists.sugarlabs.org/archive/fourthgrademath/2009-September/000337.html

Notice, on the archived message, there's a link for [the author's] spam-safe email address? That link is actually an HTML mailto link. Clicking it will create a new message to the list with a matching subject line.


Get the Message-Id from the page source

Besides downloading the month archives as mentioned at https://webapps.stackexchange.com/a/23198/51862 you can also find the Message-Id by inspecting the page source.

At the top of every message page, e.g. http://lists.busybox.net/pipermail/buildroot/2018-March/214868.html there is a mailto: link that shows as:

Ciro Santilli ciro.santilli at gmail.com

If you just click on it on Chromium 64, Ubuntu 17.10, it does not work: Thunderbird opens up, without the In-Reply-To. Same behaviour for all combinations of Firefox 58 and setting gmail as my email handler that I've tried.

However, if you open the page source, or use the Inspect browser feature (Ctrl + Shift + I), we can see that the full link is actually:


and so the In-Reply-To is actually there but URL encoded! We can then use a decoder such as: https://urldecode.org or CLI tools which gives us the correct Message-Id:

<[email protected]>

Manually set the In-Reply-To header to the Message-Id we found

Once we have the message ID, we now need to find a client that allows us to set it.

Methods that I've tested on my gmail account:

I could not find a good method for the following clients:


The RFC itself mentions that In-Reply-To in mailto links https://www.rfc-editor.org/rfc/rfc1738 :

An interesting use of your mailto URL is when browsing archives of messages. Each browsed message might contain a mailto URL like:

<mailto:[email protected]?In-Reply-
To=%[email protected]>

and it is great that GNU Mailman devs took advantage of it, but I wonder which component is not working properly to make this just work.

Confusingly, the same RFC also says:

4. Unsafe headers

The user agent interpreting a mailto URL SHOULD choose not to create a message if any of the headers are considered dangerous; it may also choose to create a message with only a subset of the headers given in the URL. Only the Subject, Keywords, and Body headers are believed to be both safe and useful.

The creator of a mailto URL cannot expect the resolver of a URL to understand more than the "subject" and "body" headers. Clients that resolve mailto URLs into mail messages should be able to correctly create RFC 822-compliant mail messages using the "subject" and "body" headers.

so maybe that's why many clients don't support it?

See also: https://stackoverflow.com/questions/4782068/can-i-set-subject-content-of-email-using-mailto/41365892#41365892

The next thing you will want to know is how to apply patch sets other people have sent to test them locally: https://stackoverflow.com/questions/5062389/getting-started-with-git-am Spoiler: it is a pain / undoable as well.

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    NOTE: of course, you can instead of editing ~/.muttrc you can run in mutt command set edit_headers=yes. Thanks for good explanation.
    – pevik
    Commented Oct 28, 2018 at 10:23

I was trying to answer to that message:


@david-z answer's helped me to understand what happens behind the scenes, but what really worked for me was going to the mailing list archive:


And downloading the compressed mbox (a .mbox file) of the mailing list archive for April 2016. Then, I imported the downloaded mbox file to Mozilla Thunderbird following these instructions:


Finally, I searched for that message and clicked on Reply to All, as suggested here:


It seems that after writing my reply and clicking on Send, my reply was actually sent to the mailing list.

  • The .mbox download is an interesting feature, but are you sure that they are using GNU Mailman / Pipermail? I cannot find that feature on the Mailman instances I've used. Commented Mar 3, 2018 at 9:13

If you can download mbox file (it's in patchwork instances, if you weren't subscribed in the past) you can get it from there. Easiest to reply to that thread is mutt -f file.mbox or load this mbox file with c in mutt.

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