We just started using mimecast for spam filtering, inbound emails works fine but problem is with the outbound emails.
Basically email should be routed through the mimecast servers but when use the mimecast's server FQDN on the send connector the email gets stuck in the queue with the 451 4.4.0 DNS query failed error ( see attached ).
I thought it was DNS issue with the exchange server and for that reason I ran a nslookup but it resolved the names properly, then I tried with telnet and I was able to connect and even to sent emails through the eu-smtp-outbound-1.mimecas
This is not a firewall issue because I am able to run telnet tests.
I have been working on this for the past 2 days but still unable to figure it out :(