[google-appengine] How to ping mailbox address before send out

Hello, When I send an email to invalid email, I got *550 5.1.1 The email account that you tried to reach does not exist.* How can i get the message before sending? I connected to smtp.gmail.com:587 send command *RCPT TO: * But I always get 250 message, until i send it out and get above 550..

[google-appengine] rcpt to: get 250

Hi, I connected to smtp.gmail.com:587 with commands: EHLO StartTLS Auth But MAIL TO: or RCPT TO: always get 250 as valid email. I want get 250 if valid and 5xx if invalid. -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe