If you get an error such as this below
Sep 12 22:41:33 ub1 postfix/smtp[12138]: 223E5385C5F7: to=<demo@berycafe.com>, relay=mailstore1.secureserver.net[72.167.238.201]:25, delay=1, delays=0.05/0/0.98/0, dsn=4.0.0, status=deferred (host mailstore1.secureserver.net[72.167.238.201] refused to talk to me: 554-p3pismtp01-004.prod.phx3.secureserver.net 554 Your access to this mail system has been rejected due to the sending MTA's poor reputation. If you believe that this failure is in error, please contact the intended recipient via alternate means.)
check the reputation by reputation
Of course substitute the search_string as required