wonder if someone could help with this query,

i host all the websites on eg. IP 66.66.66.9

and i have my name servers with the IP address.

ns1.domainname.com 66.66.66.10
ns2.domainname.com 66.66.66.11

now i want to add a reverse DNS entry,
so for which IP should i add the reverse entry ?

66.66.66.9 or 66.66.66.10 ?

thanks in advance

You should add a reverse to all IP's you use. Reverse the name server IP's to the name of the nae servers and the main IP to the servers hostname... Don't have to be nammed that way but that's simple.

The most important IP to have a reverse Dns would be your 66.66.66.9 since I believe that is where your mail server would be sending emails out from.

Since SM owns the IP block, you will need to drop them a Domain Admin ticket to have them set up the Reverse DNS for you.

SM typically assigns SOME kind of rdns to their ip's already which most mail providers should accept so there shouldn't be a 'need' for rdns changes unless you just want to.