Validating an email address before (or without) sending an email

telnet 192.168.0.6:25  'this responds with the mail server infor
helo my.domain.com 'sends request to mail server
mail from: <user@domain.com> ' you need this so their is a sender should reply ok
rcpt to: <reciever@theirdomain.com> '  this will check for a valid mailbox on that domain

For example...

220 nt.massmind.org ESMTP server (Post.Office v3.5.3 release 223 ID# 0-0U10L2S100V35) ready Tue, 11 Sep 2001 12:22:27 -0700
HELO nt.massmind.org
250 nt.massmind.org
MAIL FROM:<james@massmind.org>
250 Sender <james@massmind.org> Ok
rcpt to:<stacey@efplus.com>
550 Invalid recipient <stacey@efplus.com>
rcpt to:<sw@efplus.com>
250 Recipient <sw@efplus.com> Ok

See also:

• http://www.ex-parrot.com/~pdw/Mail-RFC822-Address.html Perl Regular Expression for validating an email address as per RFC:822^. It's only 64K long...
• http://px.sklar.com/code.html?code_id=414 (cached 20010911120204 )
• http://www.dnsreport.com/tools/mail.ch
• http://www.codeguru.com/vb/articles/2259.shtml