SMTP是用来发送电子邮件的协议。默认的通讯端口是25。与之相对就的收邮件协议是POP3
一个典型的SMTP会话如下：
telnet localhost smtp Trying 127.0.0.1... Connected to localhost. Escape character is '^]'. 220 ... ... ehlo localhost 250-... ... 250-ENHANCEDSTATUSCODES 250-PIPELINING 250-EXPN 250-VERB 250-8BITMIME 250-SIZE 250-DSN 250-ETRN 250-AUTH GSSAPI DIGEST-MD5 CRAM-MD5 250-DELIVERBY 250 HELP mail from: <[email protected]> 250 2.1.0 <[email protected]>... Sender ok rcpt to: <[email protected]> 250 2.1.5 <[email protected]>... Recipient ok data 354 Enter mail, end with "." on a line by itself this is a test message . 250 2.0.0 p9J8Ui6a010463 Message accepted for delivery quit 221 2.0.0 closing connection Connection closed by foreign host.