sendmail提出IO错误是怎么回事？

figure

有时侯邮件也能发出去，
下面是mailq的输出，但是大多数时候，好象邮件一直在那里发不出去
-----------
af@z:~$ mailq
MSP Queue status...
/var/spool/mqueue-client is empty
Total requests: 0 MTA Queue status...
/var/spool/mqueue (4 requests)
-----Q-ID----- --Size-- -----Q-Time----- ------------Sender/Recipient-----------
i641OxTt002454 201428 Sun Jul 4 09:24 <[email protected]>
(I/O error: Input/output error)
<[email protected]>
i641Mt9Y002416 201428 Sun Jul 4 09:22 <[email protected]>
(I/O error: Input/output error)
<[email protected]>
i641KlLc001921 201428 Sun Jul 4 09:20 <[email protected]>
(I/O error: Input/output error)
<[email protected]> i641HQbP001276 200723 Sun Jul 4 09:17 <[email protected]>
(I/O error: Input/output error)
<[email protected]>
Total requests: 4