I am looking to get these messages into a Bulletin Board - The most important thing I need to do is organize the messages into threads, rather than the flat listing that Yahoo! groups provides.

In order to get these messages into my bulletin board, I need to get arrange the messages into 1 mbox file per thread, or one directory per thread. I've looked at the Mail::Box modules (which seems a bit complex for my puny mind...) and Mail::MboxParser (which seems to just parse mbox files, which I've already done successfully)

Any code that I have come up with is very slow - as basically it runs a nested loop - gets the message-id for the first message, and then loops through each message in the file again checking to see if there is a matching 'in-reply-to' header, then writes them both out to a new file. This means I am processing 105k*105k messages- which takes WAY too long to do it's work.

I've tried creating a hash of message-id's, and then adding any messages with a matching 'in-reply-to' header to the relevant key - faster, but has a flaw - if a message is in reply to the 2nd or 3rd message in a thread - there is no relevant key to add it to because it isn't the start of a thread. Meaning I can only process one level deep.

All other methods I have thought of have the same flaw as the hash method described above. I am unable to think of a way to do this without processing 105k*105k messages.