1 18:41:44 localhost
sendmail[5283]: o71Afikr005283:
to=<root@localhost.localdomain>, delay=00:00:00,
xdelay=00:00:00, mailer=local, pri=31717, dsn=2.0.0, stat=Sent
后来在google上找了很多，最后终于找到原因了：
I fixed the problem by changing the hostname of my server.
Apparently "localhost.localdomain" will get rejected automatically
by a lot of mail servers. As soon as I changed my hostname to
"extra.idahostatesman.com" (a domain that is hosted on the server),
everything just worked and I had no more problems sending
e-mail.
可以用hostanme 命令临时修改主机名，hostname aa.com; 还是失败了
Aug 1 19:11:33 localhost sendmail[5579]:
o71BBVB9005579: from=root, size=221, class=0, nrcpts=1,
msgid=<201008011111.o71BBVB9005579@aa.com>,
relay=root@localhost
Aug 1 19:11:35 localhost sendmail[5580]: o71BBX3b005580:
from=<root@aa.com>, size=436, class=0, nrcpts=1,
msgid=<201008011111.o71BBVB9005579@aa.com>, proto=ESMTP,
daemon=MTA, relay=localhost [127.0.0.1]
Aug 1 19:11:35 localhost sendmail[5579]: o71BBVB9005579:
to=favorite214@139.com, ctladdr=root (0/0), delay=00:00:04,
xdelay=00:00:02, mailer=relay, pri=30221, relay=[127.0.0.1]
[127.0.0.1], dsn=2.0.0, stat=Sent (o71BBX3b005580 Message accepted
for delivery)
Aug 1 19:11:39 localhost sendmail[5582]: o71BBX3b005580:
to=<favorite214@139.com>, delay=00:00:04, xdelay=00:00:04,
mailer=esmtp, pri=120436, relay=mx.139.com. [221.176.6.96],
dsn=4.0.0, stat=Deferred: 450 Requested action not taken:cmmx01,
AS0QrJA75wiRVlVMWIvlAA--.3152S2, dynamic, reputation,
zen.spamhaus.org, please try again
切记：修改完hostname以后需要重启sendmail 服务，重启服务后，一切ok.