I wonder what's wrong with this.

maildir.coffee

fs = require 'fs'
os = require 'os'

exports.hook_rcpt = (next, connection, params) ->
    rcpt = params[0]
    rcpt_to = rcpt.address().toLowerCase()
    mail = this.config.get('mail.ini')

    connection.loginfo("hook_rcpt running through")
    if mail.accounts and mail.accounts[rcpt_to]?
        to_maildir = mail.accounts[rcpt_to]
        connection.loginfo("told mail goes to: " + to_maildir)
        connection.relaying = false
        return next(OK)
    else if mail.forward and mail.forward[rcpt_to]?
        params[0].address(mail.forward[rcpt_to])
        connection.relaying = true
        connection.loginfo("relaying mail to: " + params[0].address())
        return next(OK)
    else
        connection.relaying = false
        return next(DENY, "Mail to " + rcpt_to + " is not allowed here")

exports.hook_queue = (next, connection, params) ->
    transaction = connection.transaction
    mail = this.config.get('mail.ini')

    connection.loginfo("hook_queue running through")
    boxes = []
    pending = []
    done = []
    for rcpt in connection.transaction.rcpt_to
        rcpt_to = rcpt.address().toLowerCase()
        if mail.accounts and mail.accounts[rcpt_to]?
            to_maildir = mail.accounts[rcpt_to]
            unless to_maildir in boxes
                boxes.push(to_maildir)
    looper = (args...) ->
        if pending.length == 0 and boxes.length == 0
            return next(OK)
        else if boxes.length == 0
            return commit(pending.shift())
        else
            return receive(boxes.shift())
    receive = (to_maildir) ->
        maildir = [ mail.main.maildir_base, to_maildir ].join('/')
        tmp_path = [ maildir, 'tmp', transaction.uuid ].join('/')
        new_path = [ maildir, 'new', transaction.uuid ].join('/')
        pending.push({tmp:tmp_path, dst:new_path})

        ws = fs.createWriteStream(tmp_path)
        ws.once 'close', () ->
            looper()
        transaction.message_stream.pipe(ws)
    commit = (job) ->
        fs.link job.tmp, job.dst, (err) ->
            if err
                connection.logerror("fs.link failed on #{transaction.uuid}: " + err)
                fs.unlink job.tmp
                clean_on_fail()
                next(DENYSOFT, 'queue error')
            else
                fs.unlink job.tmp
                fs.chmod job.dst, "600"
                done.push(job)
                return looper()
    clean_on_fail = () ->
        for job in pending
            fs.unlink(job.tmp)
        for job in done
            fs.unlink(job.dst)
    return looper()

maildir.js

// Generated by CoffeeScript 1.9.3
(function() {
  var fs, os,
    indexOf = [].indexOf || function(item) { for (var i = 0, l = this.length; i < l; i++) { if (i in this && this[i] === item) return i; } return -1; },
    slice = [].slice;

  fs = require('fs');

  os = require('os');

  exports.hook_rcpt = function(next, connection, params) {
    var mail, rcpt, rcpt_to, to_maildir;
    rcpt = params[0];
    rcpt_to = rcpt.address().toLowerCase();
    mail = this.config.get('mail.ini');
    connection.loginfo("hook_rcpt running through");
    if (mail.accounts && (mail.accounts[rcpt_to] != null)) {
      to_maildir = mail.accounts[rcpt_to];
      connection.loginfo("told mail goes to: " + to_maildir);
      connection.relaying = false;
      return next(OK);
    } else if (mail.forward && (mail.forward[rcpt_to] != null)) {
      params[0].address(mail.forward[rcpt_to]);
      connection.relaying = true;
      connection.loginfo("relaying mail to: " + params[0].address());
      return next(OK);
    } else {
      connection.relaying = false;
      return next(DENY, "Mail to " + rcpt_to + " is not allowed here");
    }
  };

  exports.hook_queue = function(next, connection, params) {
    var boxes, clean_on_fail, commit, done, i, len, looper, mail, pending, rcpt, rcpt_to, receive, ref, to_maildir, transaction;
    transaction = connection.transaction;
    mail = this.config.get('mail.ini');
    connection.loginfo("hook_queue running through");
    boxes = [];
    pending = [];
    done = [];
    ref = connection.transaction.rcpt_to;
    for (i = 0, len = ref.length; i < len; i++) {
      rcpt = ref[i];
      rcpt_to = rcpt.address().toLowerCase();
      if (mail.accounts && (mail.accounts[rcpt_to] != null)) {
        to_maildir = mail.accounts[rcpt_to];
        if (indexOf.call(boxes, to_maildir) < 0) {
          boxes.push(to_maildir);
        }
      }
    }
    looper = function() {
      var args;
      args = 1 <= arguments.length ? slice.call(arguments, 0) : [];
      if (pending.length === 0) {
        return next(OK);
      } else if (boxes.length === 0) {
        return commit(pending.shift());
      } else {
        return receive(boxes.shift());
      }
    };
    receive = function(to_maildir) {
      var maildir, new_path, tmp_path, ws;
      maildir = [mail.main.maildir_base, to_maildir].join('/');
      tmp_path = [maildir, 'tmp', transaction.uuid].join('/');
      new_path = [maildir, 'new', transaction.uuid].join('/');
      pending.push({
        tmp: tmp_path,
        dst: new_path
      });
      ws = fs.createWriteStream(tmp_path);
      ws.once('close', function() {
        return looper();
      });
      return transaction.message_stream.pipe(ws);
    };
    commit = function(job) {
      return fs.link(job.tmp, job.dst, function(err) {
        if (err) {
          connection.logerror(("fs.link failed on " + transaction.uuid + ": ") + err);
          fs.unlink(job.tmp);
          clean_on_fail();
          return next(DENYSOFT, 'queue error');
        } else {
          fs.unlink(job.tmp);
          fs.chmod(job.dst, "600");
          done.push(job);
          return looper();
        }
      });
    };
    clean_on_fail = function() {
      var j, job, k, len1, len2, results;
      for (j = 0, len1 = pending.length; j < len1; j++) {
        job = pending[j];
        fs.unlink(job.tmp);
      }
      results = [];
      for (k = 0, len2 = done.length; k < len2; k++) {
        job = done[k];
        results.push(fs.unlink(job.dst));
      }
      return results;
    };
    return looper();
  };

}).call(this);