Mail delivery failed: returning message to sender

Im receiving the following error. How do I fix it?

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:

  gkimbro@earthlink.net

    host mx04.earthlink-vadesecure.net [147.135.98.120]

    SMTP error from remote mail server after pipelined sending data block:

    550 5.7.1 Sender rejected - ELNK001_304 - https://postmaster-earthlink.vadesecure.com/inbound_error_codes/#_304