I smell a future spammer. I hate spam with a passion. The
only true way to answer the question is: Send an email to the
email address, if it gets returned undeliverable then it dosn't
exist. This isn't 100% though as some email servers drop
traffic from specific countries by IP range and simply do not
reply.

Further methods: There are various methods to attain
what you are attempting to do. All used by spammers and
none appreciated by the world at large. I dont know a single
systems admin that wouldnt be willing to hang a spammer
without question or remorse.

Else, contact the systems/domain administrator and ask, if you
have a valid need you will get an answer, else you will be ignored
and dropped and added to the long list of bad bad IPs on the net.