How can I search a mail server for email addresses?

Answer 1

I am guessing that you are not the owner of the mail server. Don't do it because it could be illegal. It is called a "directory harvesting attack".

Security companies spend a lot of money protecting their mail servers from people like you.

http://www.postini.com/press/pr/pr081302.html
"In a DHA, spammers attempt to deliver messages to multiple addresses, such as [e-mail], [e-mail], and [e-mail]. Addresses that are not rejected by the receiving mail server are determined as being valid. These valid email addresses are compiled into lists and are repeatedly sold to other spammers. A successful DHA can net a spammer thousands of corporate email addresses in just a few minutes."