Based upon the error message it would appear that you need to configure reverse DNS lookups for the host. This is normally done with a PTR record. For example you might have a host mail.example.com

mail.example.com IN A 192.0.2.1


and a PTR record

1.2.0.192.in-addr.arpa. IN PTR mail.example.com


change Domain MX
I am curious if anyone uses a skiing helmet for winter biking? Would this be safe? Are skiing helmets designed to protect you from the same kind of accidents that you would have on a bike?  

My thinking is that a ski helmet would:


Help to keep your ears warm
Would fit well with ski goggles (which fit poorly with my bike helmet)
Not have air vents in it which make you cold in the winter

