r: 250-fred fonebone <fonebone@usc-isiq.arpa>
r: 250-xenon y. zither <xyz@mit-ai.arpa>
r: 250-quincy smith <@usc-isif.arpa:q-smith@isi-vaxa.arpa>
r: 250-<joe@foo-unix.arpa>
r: 250 <xyz@bar-unix.arpa>
s: quit
r: 221 mit-ai.arpa service closing transmission channel
第二步：扩展第二个列表
r: 220 mit-mc.arpa simple mail transfer service ready
s: helo su-score.arpa
r: 250 mit-mc.arpa
s: expn interested-parties
r: 250-al calico <abc@mit-mc.arpa>
r: 250-<xyz@mit-ai.arpa>
r: 250-quincy smith <@usc-isif.arpa:q-smith@isi-vaxa.arpa>
r: 250-<fred@bbn-unix.arpa>
r: 250 <xyz@bar-unix.arpa>
s: quit
r: 221 mit-mc.arpa service closing transmission channel
第三步：通过转发主机向包括于两个列表中的所有用户发送邮件
r: 220 usc-isie.arpa simple mail transfer service ready
s: helo su-score.arpa
r: 250 usc-isie.arpa
s: mail from:<account.person@su-score.arpa>
r: 250 ok
s: rcpt to:<@usc-isie.arpa:abc@mit-mc.arpa>
r: 250 ok
s: rcpt to:<@usc-isie.arpa:fonebone@usc-isiqa.arpa>
r: 250 ok
s: rcpt to:<@usc-isie.arpa:xyz@mit-ai.arpa>
r: 250 ok
s: rcpt
to:<@usc-isie.arpa,@usc-isif.arpa:q-smith@isi-vaxa.arpa>
r: 250 ok
s: rcpt to:<@usc-isie.arpa:joe@foo-unix.arpa>
r: 250 ok
s: rcpt to:<@usc-isie.arpa:xyz@bar-unix.arpa>
r: 250 ok
s: rcpt to:<@usc-isie.arpa:fred@bbn-unix.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 usc-isie.arpa service closing transmission channel
-------------------------------------------------------------
转发的情况
-------------------------------------------------------------
r: 220 usc-isif.arpa simple mail transfer service ready
s: helo lbl-unix.arpa
r: 250 usc-isif.arpa
s: mail from:<mo@lbl-unix.arpa>
r: 250 ok
s: rcpt to:<fred@usc-isif.arpa>
r: 251 user not local; will forward to <jones@usc-isi.arpa>
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 usc-isif.arpa service closing transmission channel
-------------------------------------------------------------
-------------------------------------------------------------
第一步：尝试第一台主机上的邮箱
r: 220 usc-isif.arpa simple mail transfer service ready
s: helo lbl-unix.arpa
r: 250 usc-isif.arpa
s: mail from:<mo@lbl-unix.arpa>
r: 250 ok
s: rcpt to:<fred@usc-isif.arpa>
r: 251 user not local; will forward to <jones@usc-isi.arpa>
s: rset
r: 250 ok
s: quit
r: 221 usc-isif.arpa service closing transmission channel
第二步：尝试第二台主机上的邮箱
