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I need to stop the duplicate mail (which is already in my mail box) in Thunderbird or any mail box.

Are there any filters for this?

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migrated from Jul 1 '10 at 15:02

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Not sure I understand why you are receiving duplicate mail. Are you leaving the option on your mail account to leave a copy on the server? Or is there some other problem that I am not understanding? – spinon Jul 1 '10 at 6:57
In my case, if I receive an email addressed to me that's also addressed to a mailing list that I'm on I receive two copies. I'd love to only get one of them.... – Joe Casadonte Jul 6 '10 at 12:17
Try checking your user profile folder under C:\Users\username\AppData\Roaming\Thunderbird. Maybe you can see something there. If that's a no go, try upgrading to 3.0.5 AND/OR delete the mails and redownload them. – Shiki Jul 20 '10 at 15:37
@Shiki what would I look for? Also, there is nothing wrong with the e-mails so redownloading them won't fix anything, just loose all the sorting I've done. – BCS Jul 20 '10 at 20:08

How about the "Remove Duplicate Messages" plugin for Thunderbird?

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I believe there's more development effort behind the "Alternate" version of the "Remove Duplicate Messages" add-on. (Last update March 11, 2011 as of this writing). This is the one I use.

Note that it refuses to work on "special" folders by default, and you have to enable this option in the settings: → "Message Comparison" tab → UNcheck "Skip Special Folders (Sent, Drafts etc.)."

I've used this extension on several thousand messages at once (merging mail archives from different mail clients that had used POP to fetch mail) and it hasn't burned me yet. You probably won't want to try it on one of Thunderbird 3's new "unified" folders, as I'm not sure that will turn out too well. Rather, switch to the "All Folders" view and select two individual folders using the context menu option Set original message folder(s) for next duplicate search.

And make backups.

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P.S.: Forgot to mention that Mutt, naturally, has this capability baked right in. Press the tag-pattern key ("T" by default), then ~= (tilde, equals) as the pattern. The you can operate on the "tagged" messages by prefixing a regular mail command (like 'd' for delete) with ; (semicolon), which means "do whatever I say next on all tagged messages." If you have trouble finding duplicates with threaded conversations, try starting here for a solution:…. – TheDudeAbides Mar 28 '11 at 1:46
There is more development effort - mine :-) – einpoklum Nov 17 '12 at 17:28

There is NO NEED for an extension.

There's a config option in thunderbird that you set to deal with duplicate messages. You can delete, move to trash or mark as read if you don't want them appearing in your inbox like normal mail (who would? I don't know why this isn't set to trash by default).

GHacks has an article on it:

Basically, access config editor via the advanced options tab and edit the mail.server.default.dup_action flag.

0 = keep dupe. 1 = delete dupe. 2 = move dupe to trash. 3 = mark dupe as read.

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Try reading this

It has a couple of suggestions for extensions to delete duplicates and also has some tips on avoiding them in the first place.

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The kind of de-duping that you're asking for is usually configured on the server. For example, one can configure Microsoft Exchange to recognize that a particular user is also on a distribution list, and only send one copy:

On the client side, your only real option is to create a filter. Differentiating the two emails is not immediately obvious to me. Here's what I would do:

  1. In firefox, double click both emails to open them in separate tabs
  2. For each email, choose View->Headers->All
  3. Compare the headers in both and see if you can determine a differentiating factor
  4. If you succeed in (3), then create a custom filter and delete the message based upon the header.
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