What is an email reverse lookup and what is it used for?
Does it strictly provide who owns that email address. Surely privacy isnt invaded.
Do you mean "Reverse DNS Lookup?"
In regards to e-mail, you can look at the e-mail headers and find out where the e-mail originated whether the e-mail was sent out legitimately or by some spam-bot working on some zombie computer.
If you mean "Reverse DNS Lookup", it’s a way of finding the hostname or host associated with a given IP address or host address.
Typically, the DNS is used to determine what IP address is associated with a given hostname; so, to reverse resolve a known IP address is to lookup what the associated hostname is belonging to that IP address.
A reverse lookup is often referred to as reverse resolving, or more specifically reverse DNS lookup, and is accomplished using a "reverse IN-ADDR entry" in the form of a PTR record