#!/usr/bin/python

from btsutils.debbugs import debbugs
import mailbox
import re
import sys

mailbox =  mailbox.Maildir(sys.argv[1], factory=False)
bts = debbugs()

for key in mailbox.keys():
    message = mailbox[key]
    if not 'S' in message.get_flags():
        if message['X-Debian-PR-Message']:
            try:
                bugnr = message['X-Debian-PR-Message'].split()[1]
            except IndexError:
                continue
        else:
            test = re.search('Bug#(\d{6})', message['Subject'])
            if test:
                bugnr = test.group(0)[4:]
            else:
                continue

        try:
            bug = bts.get(bugnr)
        except AttributeError:
            print bugnr
            continue

        if bug.getStatus() == u'done':
            message.set_flags(message.get_flags() + 'S')
            mailbox[key] = message


mailbox.flush()

Run it like python cleanbugsmail.py ~/Maildir/.debian.bugs. Anyone aware of a better solution?