This message was created automatically by mail delivery software. A message that you sent could not be delivered to one or more of its recipients. This is a permanent error. The following address(es) failed: email@example.com SMTP error from remote mail server after end of data: host mailin-02.mx.aol.com [22.214.171.124]: 421-: (DNS:NR) http://postmaster.info.aol.com/errors/421dnsnr.html 421 SERVICE NOT AVAILABLE: retry timeout exceeded My customer's domain does have a reverse dns record setup, over 2 days now. Why else would she continue to get this error?