Is there any open source tool that automatically detects email streams such as Gmail?

Question

For example, if the original message (message 1) ...

Hey John,
Want to go get some pizza?
-Bill

And the answer (message 2) ...

Bill,
Sorry, I can't have lunch today.
Jonathan Parks, CTO Acme Systems

On Wed, February 24, 2010 at 16:43, Bill Waters wrote:

Hey John,
> Want to go get some pizza?
> -Bill

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Answer 1

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http://www.jwz.org/doc/threading.html

Answer 2

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On Wed, Feb 24, 2010 at 4:43 PM, Bill Waters wrote:

Pizza tomorrow Re: Pizza tomorrow . FW: RE: ( ).

Answer 3

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Answer 4

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? IMAP?

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RFC 5256.

Answer 5

sup http://freshmeat.net/articles/sup-gmail-meets-the-console, ,