I've owned sporty.org for a long time. Almost 10 years now. I get a lot of spam and legit email to the email addresses I maintain on it. I use this script to server-side filter mail into folders for me. It's for use with qmail using Maildir format. It's short enough that it should be self explanitory.

If I was smart, I'd make it a daemon with a c-written lightweight client. Bah, I'm not annoyed enough yet. :)

use File::Temp;
use Mail::Internet;
use strict;

my $folderList = undef;
open( $folderList, ".folderFilter" );
my @folders = <$folderList>;

my @mail = <>;
my $message = Mail::Internet->new( \@mail );
my $mailFrom = $message->head->get("From");

# The RFC says one thing, but sometimes, people leave it out.
$mailFrom = $1 if( $mailFrom =~ /<(.*?)>/ );

foreach my $folder ( @folders )
{
    my( $folder, $from ) = split( /\|/, $folder );
    if( $from =~ /\Q$mailFrom\E/ )
    {
        writeMail( "Maildir/$folder/new" );
        exit( 0 );
    }
}

writeMail( "Maildir/.unrecognized/new" );

sub writeMail
{
    my $folder = shift;
    my $timestamp = time();
    my $fileHandle = new File::Temp( TEMPLATE => "$timestamp.XXXXXX", 
+DIR=> $fol
der, UNLINK => 0 );
    $message->print( $fileHandle );
    close( $fileHandle );
}
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