[Dovecot] Removal of mailist duplicates?

[Peter Bell]

I am using mpop to fetch mail from my service provider (who use dovecot).

I use dovecot to hold all my mail on a local slackware server, with 
sieve filters, based on 'List-Id', directing mailist postings to their 
own folders.

I use thunderbird to read my mail on an ubuntu desktop.

When I receive a reply to a posting I make to a mailist (such as this 
one), replies I receive are usually sent to me with cc to the list.

I would expect, then, to receive the message twice - once in my personal 
mailbox, and once to the mailist folder.  However, this doesn't happen - 
I only see the posting in the mailist folder.

Can anyone tell me at which stage in the process the other message is 
being supressed?

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Peter Bell                                Mob: +63 (0) 9287 340 343
Tagum City, Philippines.                  Tel: +63 (0) 84 400 5085
email/msn: peter at bellfamily.org.uk        Tel: +44 (0) 118 331 0000