如何用 SMTP 命令，远程登录到服务器上发送邮件？

如何用 POP3 命令，直接在服务器上操作邮件？
如何用 SMTP 命令，远程登录到服务器上发送邮件？

端口测试：

# telnet mail.easy.com 25 （测试25端口）
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
220 mail.easy.com ESMTP Postfix
quit
221 Bye
Connection closed by foreign host.

# telnet mail.easy.com 110 （测试110端口）
Trying 127.0.0.1...
Connected to localhost.localdomain (127.0.0.1).
Escape character is '^]'.
+OK dovecot ready.
quit
+OK Logging out
Connection closed by foreign host.

如何用 SMTP 命令，远程登录到服务器上发送邮件？

telnet 登陆服务器的 25 端口，执行 SMTP 命令： HELO
或者：EHLO
MAIL FROM：<[email protected]>
RCPT TO: <[email protected]>
DATA
QUIT
如何用 POP3 命令，直接在服务器上操作邮件？ telnet 登陆服务器的 110 端口，执行 POP3 命令： USER
PASS
LIST [msg]
TOP [msg] [count_n]
UIDL [msg]
APOP name digest
DELE [msg]
NOOP
QUIT