5.1.2 SMTP; 550 Host unknown - Email Bounce
Posted on 2016-09-14
First time I have posted in here so be nice :)
5.1.2 SMTP; 550 Host unknown
one of my customers is having email bounce back issues, have done multiple checks with RBL and other , nothing is coming up blocked.
Current server is a SBS 2011 with exchange 2010. it doesn't happen to every email only some and has got me stumped as to why this is happening .