function pruneCommittedDiffs(mailbox, dest_mailbox)
  diff_set = mailbox:contain_subject('[Differential]')
  committed_diff_set = diff_set:contain_field('X-Phabricator-Mail-Tags', '<differential-committed>')
  for _, message in ipairs(committed_diff_set) do
    mmbox, uid = table.unpack(message)
    rev_key = string.gsub(mmbox[uid]:fetch_field('In-Reply-To'), 'In%-Reply%-To: ', '')
    all_diff_msgs = diff_set:contain_field('In-Reply-To', rev_key) + diff_set:contain_field('Message-ID', rev_key)
    all_diff_msgs:move_messages(dest_mailbox)
  end
end