s: on tuesday.
s: john.
s: .
r: 250 ok
s: quit
r: 221 usc-isie.arpa service closing transmission channel
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确认和发送
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r: 220 su-score.arpa simple mail transfer service ready
s: helo mit-mc.arpa
r: 250 su-score.arpa
s: vrfy crispin
r: 250 mark crispin <admin.mrc@su-score.arpa>
s: send from:<eak@mit-mc.arpa>
r: 250 ok
s: rcpt to:<admin.mrc@su-score.arpa>
r: 250 ok
s: data
r: 354 start mail input; end with <crlf>.<crlf>
s: blah blah blah...
s: ...etc. etc. etc.
s: .
r: 250 ok
s: quit
r: 221 su-score.arpa service closing transmission channel
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获得和发送邮件 首先确定用户名，然后尝试将邮件发送到用户终端，当它失败时，发送到用户邮箱。
-------------------------------------------------------------
r: 220 su-score.arpa simple mail transfer service ready
s: helo mit-mc.arpa
r: 250 su-score.arpa
s: vrfy crispin
r: 250 mark crispin <admin.mrc@su-score.arpa>
s: send from:<eak@mit-mc.arpa>
r: 250 ok
s: rcpt to:<admin.mrc@su-score.arpa>
r: 450 user not active now
s: rset
r: 250 ok
s: mail from:<eak@mit-mc.arpa>
r: 250 ok
s: rcpt to:<admin.mrc@su-score.arpa>
r: 250 ok
s: data
r: 354 start mail input; end with <crlf>.<crlf>
s: blah blah blah...
s: ...etc. etc. etc.
s: .
r: 250 ok
s: quit
r: 221 su-score.arpa service closing transmission channel
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上述问题的更有效的作法
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r: 220 su-score.arpa simple mail transfer service ready
s: helo mit-mc.arpa
r: 250 su-score.arpa
s: vrfy crispin
r: 250 mark crispin <admin.mrc@su-score.arpa>
s: soml from:<eak@mit-mc.arpa>
r: 250 ok
s: rcpt to:<admin.mrc@su-score.arpa>
r: 250 user not active now, so will do mail.
s: data
r: 354 start mail input; end with <crlf>.<crlf>
s: blah blah blah...
s: ...etc. etc. etc.
s: .
r: 250 ok
s: quit
r: 221 su-score.arpa service closing transmission channel
-------------------------------------------------------------
邮件列表 首先，两个邮件列表中的每一个在不同主机的不同会话上扩展，然后，通过转发主机向列表上的用户发送邮件。
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第一步：扩展第一个列表
r: 220 mit-ai.arpa simple mail transfer service ready
s: helo su-score.arpa
r: 250 mit-ai.arpa
s: expn example-people
r: 250-<abc@mit-mc.arpa>
