$./a.out smtp.gmail.com 25
220 mx.google.com ESMTP 9sm2923369yxf.23

250 mx.google.com at your service

220 2.0.0 Ready to start TLS

after handshake
Common Name: smtp.gmail.com
after get cert dn
-----BEGIN SSL SESSION PARAMETERS-----
d4f65cac7d180d5b17d3f6334cf60bcaee84cea782dc39be68e9224d06ec9b86
-----END SSL SESSION PARAMETERS-----
CIPHER is RC4-MD5

EHLO
250-mx.google.com at your service, [61.11.23.15]
250-SIZE 35651584
250-8BITMIME
250-AUTH LOGIN PLAIN
250-ENHANCEDSTATUSCODES
250 PIPELINING
MAIL FROM:<root@stripe>
502 5.5.1 Unrecognized command. 9sm2923369yxf.23


Above program just connect to smtp.gmail.com@25 and send
1) HELO
2) STARTTLS
..
After succ handshake we need to send EHELO again. I have sent EHELO but after that whne I semt MAIL FROM it give me unrecognized command why?

Hello,

Although you can telnet to Google SMTP server on port 25, you cannot send mails using that port. Google only accepts mails on port 465 instead of 25. That's why the command is failing. If you have a Gmail account yourself, check under Settings, Forwarding and POP/IMAP, configuration instructions. There you'll find the necessary information.

Kind regards,

Eric