Email Problem (421 Requested action aborted)

Hi, Please help regarding below error code, it happen to one of my client. Any clue what it is and how to fix it? Email already in queue for more than 2 days now. Thanks you very much. -------------------- Subject: Warning: message 1XW5Ur-0003VS-K9 delayed 24 hours This message was created automatically by mail delivery software. A message that you sent has not yet been delivered to one or more of its recipients after more than 24 hours on the queue on dc.howwel.pw. The message identifier is: 1XW5Ur-0003VS-K9 The subject of the message is: Re: Bebe au lait New Order The date of the message is: Mon, 22 Sep 2014 22:25:26 +0700 The address to which the message has not yet been delivered is: ....@.....com Delay reason: SMTP error from remote mail server after initial connection: host mx01.1and1.com [74.208.5.21]: 421-perfora.net (mxeueus001) Nemesis ESMTP Service not available 421 Requested action aborted: local error in processing