Email SMTP validator

Question

I need to send hundreds of newsletters, but would like to check first if email exists on server. It\'s called SMTP validation, at least I think so, based on my research on I

Answer 1

SMTP is a text based protocol carried over TCP/IP.

Your validation program needs to open a TCP/IP connection to the server's port 25 (SMTP), write in a few lines and read the answer. Validation is done (but not always) on the "RCTP TO" line and on the "VFRY" line.

The SMTP RFC describes how this works (see Green@Beta.ARPA below, S are lines sent by the client, R are lines received from the server):

Example of the SMTP Procedure

         This SMTP example shows mail sent by Smith at host Alpha.ARPA,
         to Jones, Green, and Brown at host Beta.ARPA.  Here we assume
         that host Alpha contacts host Beta directly.

            S: MAIL FROM:
            R: 250 OK

            S: RCPT TO:
            R: 250 OK

            S: RCPT TO:
            R: 550 No such user here