SMTP mail gateway test

How to test if SMTP email gateway or server is accepting or relaying your emails successfully using commandline option through telnet from Unix or Windows platforms.

telnet emailgateway.example.com smtp
220 emailgateway.example.com ESMTP Postfix EHLO localhost
250-emailgateway.example.com
250-PIPELINING
250-SIZE 10240000
250-VRFY
250-ETRN
250 8BITMIME MAIL FROM: <testadmin@example1.com>
250 Ok RCPT TO: <unknown@unknowndomain.com>
554 <unknown@unknowndomain.com>: Relay access denied RCPT TO: <unknown@example1.com>
554 <unknown@example.com>: Relay access denied RCPT TO: <user1@example1.com>
250 Ok DATA
354 End data with <CR><LF>.<CR><LF> Subject: test
test 1 2 3
.
250 Ok: queued as 5152A39097 QUIT
221 Bye