Let's say your server IP is 211.147.9.106
1 First, you should know which DNS server is responsible for this IP's reverse domain name resolution. You can use this page to query reverse domain name resolution information http://www.dnsstuff.com/tools/ptr.ch?ip=211.147.9.106
Look at the last paragraph.
Details:
ns.cnc.ac.cn. (a authoritative nameserver for 147.211.in-addr.arpa., which are in charge to the reverse DNS for 211.147.9.106)
says that there are no PTR records for 211.147.9.106.
To the reverse DNS set up for 211.147.9.106, you need to speak to your Internet provider. You could also
Check with sun@cnnic.cn., who's in charge of the 147.211.in-addr.arpa. Zone.
Probably means you need to contact ns.cnc.ac.cn, ns.cnc.ac.cn is responsible for 211.147.9.106 's reverse domain resolution.
2 Then you can ask your IP provider, that is, your hosting provider, if your business users have fixed IP, you should find telecom. Want them to contact with ns.cnc.ac.cn, give you this IP plus reverse domain name resolution records, generally this IP reverse resolution to your mail server corresponding MX record.