451 4.4.0 DNS query failed Microsoft Exchange 2010https://i2.wp.com/windowstechblog.nl/wp-content/uploads/2015/02/5.png?fit=1024%2C149&ssl=1https://i2.wp.com/windowstechblog.nl/wp-content/uploads/2015/02/5.png?resize=150%2C81&ssl=1Martien van Dijkit's all about Microsoft