Mail sending problem using php 7.0

Hi.. as per mentioned in this link to check php is sending mail or not (https://easyengine.io/tutorials/php/test-email-sending/). I am using ubuntu 16.04 so i tried that command as mentioned php -a and after that mail ('mail id', "Test Postfix", "Test mail from postfix");. i am not getting any error msg there in console but when I check my log.mail file it says me (Helo command re$
and rejected: need fully-qualified hostname (in reply to RCPT TO command))) even m not getting any mail so could you please help me regarding so that i can fix my problem ...thnks