When getting a delivery status notification (Failure) this snippet is included into the message:
Technical details of permanent failure: Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 5.1.1 User unknown (state 13).
So this means I guess that before sending the mail google made a query if the target mail server will accept it. How could I reproduce this query?
In other words, I would like to manually query a mail server if an address exits or not. How do I do this?