Opencart developer Fix small issue with SMTP email server

I am getting error when sending emails from website through "SMTP" Can someone fix? Maybe i'll choose them for lifetime our web developer. Error " Fatal error: Uncaught exception 'Exception' with message 'Error: DATA not accepted from server!' in /home/tampri5/public_html/system/library/[login to view URL] Stack trace: #0 /home/tampri5/public_html/catalog/model/checkout/[login to view URL](658): Mail->send() #1 [internal function]: ModelCheckoutOrder->addOrderHistory(28, '15') #2 /home/tampri5/public_html/system/storage/modification/system/engine/[login to view URL](178): call_user_func_array(Array, Array) #3 [internal function]: Loader->{closure}(Array, Array) #4 /home/tampri5/public_html/system/engine/[login to view URL](25): call_user_func_array(Object(Closure), Array) #5 /home/tampri5/public_html/catalog/controller/extension/payment/[login to view URL](1430): Proxy->__call('addOrderHistory', Array) #6 /home/tampri5/public_html/catalog/controller/extension/payment/[login to view URL](1430): Proxy->addOrderHistory(28, '15') #7 [internal function]: ControllerExtensionPaymentPPExpress->checkoutReturn() #8 /home/tampri5/public_html/system/storage/modification/system/engine/[login to view URL](51): call_user_func_array(Ar in /home/tampri5/public_html/system/library/[login to view URL] on line 409 "