I've got a large number of mbox-format mailboxes here, accumulated over the years of mail backups upon mail backups. I'm trying to go through them all and remove any duplicate messages that may be in them, before finally archiving them to permanent offline storage. I've been putting them in more granular heirarchies over the years, so there may be ~mail/foo, then later may become ~mail/Projects/foo, which contains mostly the same mail, but could be different.

What I need to do is roll through each one, and yank out the duplicate emails that may have been put there from concatenating them or testing/debugging broken procmail recipes, and store them each in a single mbox file that contains only unique mail.

I've looked into Mail::Box::Mbox and Email::Folder::Mbox, but decided to try to roll my own first. Here's what I've got, and it seems to work so far. 

use strict;

undef $/;
my %seen;
my @para          = split /(\n\n+)/, <>;

while (defined($_ = shift @para)) {
    die "No From line!\n" unless /^From /;

    my ($id)      = map /^Message-ID:\s(\S.*)/im, 
                    split /\n(?! )/;

    warn "No Message-ID! [[$_]]\n" unless defined $id;
    $_ .= shift @para while @para and $para[0] !~ /^From /;
    print unless defined $id and $seen{$id}++;
}

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Comments? Improvements?

In reply to Parsing out "unique" messages from mbox files by hacker

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