Mail stucked in /var/spool/mqueue

Problem:
Thousands of mails are stucked in /var/spool/mqueue

Solution:

Manually test sendmail:

sendmail -v -q
Warning: .cf file is out of date: sendmail AIX5.3/8.13.4 supports version 10, .cf file is version 9

Running /var/spool/mqueue/n3RLGNaZ195422 (sequence 1 of 30)
dtuser... Connecting to local...
dtuser... Deferred: local mailer (/bin/bellmail) exited with EX_TEMPFAIL

Running /var/spool/mqueue/n3RLHQDC198652 (sequence 2 of 30)
dtuser... Connecting to local...
dtuser... Deferred: local mailer (/bin/bellmail) exited with EX_TEMPFAIL

Check permission of /var/spool/mail and /var/spool/mqueue

ls -ld /var/spool/mail
drwxr-xr-x 2 bin mail 512 Jul 30 2007 /var/spool/mail
ls -ld /var/spool/mqueue
drwxrwx--- 2 root system 6376448 Apr 27 14:47 /var/spool/mqueue

Permission of /var/spool/mail should be 775.

chmod 775 /var/spool/mail

Now problem is solved.

sendmail -v -q
Warning: .cf file is out of date: sendmail AIX5.3/8.13.4 supports version 10, .cf file is version 9

Running /var/spool/mqueue/n3RLYND7164390 (sequence 1 of 32)
dtuser... Connecting to local...
dtuser... Sent

Running /var/spool/mqueue/n3RLZQLo185340 (sequence 2 of 32)
dtuser... Connecting to local...
dtuser... Sent

Running /var/spool/mqueue/n3RLaUAI198578 (sequence 3 of 32)
dtuser... Connecting to local...
dtuser... Sent

Running /var/spool/mqueue/n3RLbWZV198618 (sequence 4 of 32)
dtuser... Connecting to local...
dtuser... Sent