554 5.7.1 This message has been blocked because the return email domain is invalid.(failed to obtain DNS record for domain)

[Wim Groen]

Hi guys,
 
Hope you can help me out. I've setup a new hosting
server(hosting.example.com) all notification of that server i redirect
to my postfix smtp server. When i look in the postfix log i see the
message:
554 5.7.1 This message has been blocked because the return email domain
is invalid.(failed to obtain DNS record for domain hosting.example.com.
I created a A record for hosting.example.com and i created a PTR record
for hosting.example.com. What did I do wrong?
 
Kind Regards,
 
Wim Groen