SMTP Protocol (sonet.all@gmail.com) 1. Find MX Record nslookup > set q=mx > program.com.tw Server: 127.0.1.1 Address: 127.0.1.1#53 Non-authoritative answer: program.com.tw mail exchanger = 5 se2.program.com.tw. program.com.tw mail exchanger = 10 mail.program.com.tw. < > nslookup -q=mx yahoo.com nslookup -q=mx google.com 2. SMTP Protocol (Simple Mail Transfer Protocol) a. http://tools.ietf.org/rfc/rfc821.txt b. http://tools.ietf.org/html/rfc5321 b. Example of the SMTP Procedure S: EHLO program.com.tw R: 250-se2.program.com.tw 250-PIPELINING 250-8BITMIME 250 SIZE 52428800 S: MAIL FROM: R: 250 OK S: RCPT TO: R: 250 OK S: RCPT TO: R: 504 Authentication failed for SMTP service. --> (system logout) S: RCPT TO: R: 550 User (test_account@program.com.tw) unknown. S: DATA R: 354 Start mail in...