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I use Thunderbird's threaded view of email messages to group emails together which are related. However, sometimes people will reply to messages using some mail program which does not properly set the headers to tell it's a reply, or will even write a new mail instead of replying.

In these cases I would like to manually assign or "dock" a mail to an existing thread. Is there some way / addon to do this in Thunderbird?

I'm thinking along the lines of a context menu "attach mail to thread XXX". The mail would then become part of that thread (maybe with a special marker explaining that it was manually grouped).

Update: I'm using Thunderbird 3.7 Alpha, but I'm interested in solutions for any version.

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The feature request for this is over at… . Please go and +1 it! :) – colan Sep 20 '13 at 15:34
And the actual ticket for this is over at . – colan Sep 20 '13 at 15:43
plugin for this: – silvio Dec 21 '15 at 9:00
up vote 7 down vote accepted

The only solution I can think of is to change the subject-line so that the email would fit into Thunderbird's thread-model (Re: subject). There are two way I can think of:

  1. Forward the email to yourself with a new subject-line.

  2. Use the TB Header Tools Extension to edit the subject-line. However, I have no experience with this extension and cannot guarantee that it works. Apparently, it used to work pretty well with TB2.

[EDIT] The TB Header Tools Extension is not available for current versions of Thunderbird.
I now recommend EditEmailSubject which I use myself with no problems.

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Thanks for the pointer to the Header Tools Extension. Apparently it really does not work for TB 3, but it might give me an idea. – sleske Apr 12 '10 at 10:44
I have Thunderbird gouping messages with DIFFERENT subject lines:… – That Brazilian Guy Sep 24 '13 at 17:58
Yes, Thunderbird has evolved since 2010. – harrymc Sep 24 '13 at 18:33
These days hust we use <>; for this. see answer: – silvio Dec 21 '15 at 8:42
Except that comments say it's broken. – Peter Flynn Apr 12 at 13:00

Please check a good info on threading here:

Main reason for unwanted behaviour?:

Unrelated threads are grouped together!

Someone was lazy, and instead of composing a new message, just hit "Reply All", and changed the subject. You need to educate these people and tell them not to use reply all when they intend to start a new thread.

I'm still wondering whether there is a way to manually change the reply-to or references headers.

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Yes, there is a way to manually change the reply-to headers. See my answer :-). – sleske Oct 13 '11 at 12:48
All that is required is to be able to drag an orphan message and drop it onto the thread where it ought to have been in the first place if the sender had had the wit to use Reply instead of New... – Peter Flynn Apr 12 at 13:00

You can use the Header Tools Lite plugin by genius Paolo.

- select message under which to Thread
- message_context_menu>HeaderToolsLite>Change Header Details
- copy Message-ID: (or one of References: to thread randomly)
- select misplaced message
- message_context_menu>HeaderToolsLite>Change Header Details
- paste into References: in comma separated list
- thank
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For this, I use TotalMessage extension. Drag a message to the desired parent message and drop it.

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TotalMessage would be really great, but it has broken UI (TotalMessage 3.1 in TB 38.5.1 under Linux) and left a horrendous mess after its removal. – Palec Jan 10 at 22:26
It tries to do way too much. All that is required is to be able to drag an orphan message and drop it onto the thread where it ought to have been in the first place if the sender had had the wit to use Reply instead of New... – Peter Flynn Apr 12 at 12:59

harrymc's answer pointed me to a review post for the TB Header Tools Extension, which says:

However, I have discovered that TB3 now DOES allow the email to be dragged onto the desktop, edited with Notepad, and dragged back, so that's my preferred way now.

This is probably what I'll do as well. That way I can change/add headers as I see fit (either adjust the subject, or directly add the missing In-Reply-To: or References: header.

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@sleske: Since you've added your own answer, we now certainly have a problem with the bounty. This is why the poster is always encouraged to edit his post, rather than adding answers, if there's a bounty or not. – harrymc Apr 12 '10 at 20:09
@harrymc: Sorry, didn't know that. Where is the problem? I can just accept an answer, can't I? – sleske Apr 12 '10 at 23:35
Righty-o, that's one way to solve the problem. However, my answer is not the one that you'll use :) – harrymc Apr 13 '10 at 20:20
@harrymc: Well, no, not directly, but you did point me into an interesting direction. At any rate, there is definitely no better answer than yours ;-). – sleske Apr 13 '10 at 22:22

The feature request seems to date from 2000, so I don't think it's being taken at all seriously.

This feature would be at its most useful for the OP's use case as described: when a reply to a message has been written with an MUA which does not preserve the data needed for threading (eg In-Reply-To and References).

If you could drag and drop such messages onto the thread where they belong, that would fix the problem. The process would need to add the headers necessary to preserve the message's new position, and perhaps rename any headers that would interfere with that to X- variants.

  • Yes, of course it could be used to move messages with the "wrong" Subject header into seemingly unrelated threads, but I submit that that is a minority use case.

  • Yes, of course badly-educated users need better training, and badly-written MUAs need to be defended against, but that's a different problem, and not a battle that the individual can win overnight.

This one feature would result in a massive increase in productivity for heavy email users* who are probably among Thunderbird's best advocates.


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