mail error

  • Hello, I get this error, and do not receive any email from that address.
    Do you have any idea how to fix it.

    NOQUEUE: reject: RCPT from[IP Address]: 504 5.5.2 <gandalf>: Helo command rejected: need fully-qualified hostname; from=<> to=<> proto=ESMTP helo=<gandalf>
    Dec 18 17:51:55 www postfix/smtpd[22158]: disconnect from[IP Adresss]

    OpEn YouR mINd , OpeN YouR SourcE cOdE