Mailer Error SMTP Error: Data not accepted

Thanks @George, I get this error when I do what you suggest:

{"code":2,"file":"\/volume1\/web\/instance_1\/dmxConnectLib\/PHPMailer\/PHPMailer\/PHPMailer.php","line":1910,"message":"SMTP Error: data not accepted.","trace":"#0 \/volume1\/web\/instance_1\/dmxConnectLib\/PHPMailer\/PHPMailer\/PHPMailer.php(1601): PHPMailer\\PHPMailer\\PHPMailer->smtpSend('Date: Mon, 16 N...', 'This is a multi...')\n#1 \/volume1\/web\/instance_1\/dmxConnectLib\/PHPMailer\/PHPMailer\/PHPMailer.php(1437): PHPMailer\\PHPMailer\\PHPMailer->postSend()\n#2 \/volume1\/web\/instance_1\/dmxConnectLib\/modules\/mail.php(132): PHPMailer\\PHPMailer\\PHPMailer->send()\n#3 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(193): modules\\mail->send(Object(stdClass), '')\n#4 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(157): lib\\App->execSteps(Object(stdClass))\n#5 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(127): lib\\App->execSteps(Array)\n#6 \/volume1\/web\/instance_1\/dmxConnectLib\/modules\/core.php(92): lib\\App->exec(Object(stdClass), true)\n#7 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(193): modules\\core->condition(Object(stdClass), '')\n#8 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(157): lib\\App->execSteps(Object(stdClass))\n#9 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(127): lib\\App->execSteps(Array)\n#10 \/volume1\/web\/instance_1\/dmxConnectLib\/modules\/core.php(92): lib\\App->exec(Object(stdClass), true)\n#11 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(193): modules\\core->condition(Object(stdClass), '')\n#12 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(157): lib\\App->execSteps(Object(stdClass))\n#13 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(127): lib\\App->execSteps(Array)\n#14 \/volume1\/web\/instance_1\/dmxConnectLib\/modules\/core.php(90): lib\\App->exec(Object(stdClass), true)\n#15 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(193): modules\\core->condition(Object(stdClass), '')\n#16 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(157): lib\\App->execSteps(Object(stdClass))\n#17 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(127): lib\\App->execSteps(Array)\n#18 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(116): lib\\App->exec(Object(stdClass), false)\n#19 \/volume1\/web\/instance_1\/dmxConnectLib\/lib\/App.php(94): lib\\App->exec(Object(stdClass))\n#20 \/volume1\/web\/instance_1\/dmxConnect\/api\/Hot_Account\/send_ha.php(8): lib\\App->define(Object(stdClass))\n#21 {main}"}