Hack the Route Start free Open app Network services
SMTP
How mail moves: from a client to its own mail server, then from server to server, found by the domain's MX record.
A conversation on TCP 25 of commands (EHLO, MAIL FROM, RCPT TO, DATA) and three-digit replies. The sender's
server looks up the recipient domain's MX record and relays the message to the server it names, which stores it.
The envelope (MAIL FROM, RCPT TO) steers delivery; the headers (From:, To:) are what people read, and nothing
makes them agree. Each server adds a Received: header, newest on top. A server relays to other domains only for its
own users; one that relays for anyone is an open relay.