Newbieish question

[Dave Warren]

Is newbieish a word? :)

Anyway, I have my own views, but what is the "generally accepted" way to get
ahold of the owner/administrator of a machine, given the IP address, and
knowing it runs mail services?

Should I trust the rDNS?  It's SOA record?  Abuse.net for the rDNS domain?
ARIN (Or similar for that area)?  Or something else entirely?

Thanks in advance, hope it's not too off topic ;)