Mail stucked in /var/spool/mqueue
Problem:
mails get stucked in /var/spool/mqueue
Note: If this document does not resolve your problem, please check or troubleshoot your sendmail.cf configuration file.
Solution:
nimserver(/usr/spool)#ls -ld /var/spool/mail
drwxrwxr--    2 bin      mail            256 Feb 04 13:39 /var/spool/mail
nimserver(/usr/spool)#

After changing permission of /var/spool/mail to 775.

nimserver(/usr/spool)#ls -ld /var/spool/mail
drwxrwxr-x    2 bin      mail            256 Feb 04 13:39 /var/spool/mail
nimserver(/usr/spool)#

Check how many mails get stuck, in my case its just two..

nimserver(/var/spool/mqueue)#ls -ltr
total 40
-rw-------    1 root     system         5086 Feb 04 09:58 dfr14FwhRe5177576
-rw-------    1 root     system            5 Feb 04 10:01 dfr14G1ps77471166
-rw-------    1 root     system          804 Feb 04 10:18 qfr14FwhRe5177576
-rw-------    1 root     system          729 Feb 04 10:22 qfr14G1ps77471166
nimserver(/var/spool/mqueue)#

Lets push them…

nimserver(/)#sendmail -v -q
Running /var/spool/mqueue/r14G1ps77471166 (sequence 1 of 2)
afzal_tahir@yourdomain.com... Connecting to smtp01.yourdomain.com. via relay...
220 smtp01.yourdomain.com ESMTP Service (Lotus Domino Release 8.5.2FP2 HF252) ready at Mon, 4 Feb 2013 14:50:56 -0500
>>> EHLO nimserver.yourdomain.com
250-smtp01.yourdomain.com Hello nimserver.yourdomain.com ([192.168.2.30]), pleased to meet you
250-HELP
250-SIZE 25600000
250 PIPELINING
>>> MAIL From:<afzalt@nimserver.yourdomain.com> SIZE=412
250 afzalt@nimserver.yourdomain.com... Sender OK
>>> RCPT To:<afzal_tahir@yourdomain.com>
>>> DATA
250 afzal_tahir@yourdomain.com... Recipient OK
354 Enter message, end with "." on a line by itself
>>> .
250 Message accepted for delivery
afzal_tahir@yourdomain.com... Sent (Message accepted for delivery)
Running /var/spool/mqueue/r14FwhRe5177576 (sequence 2 of 2)
>>> RSET
250 Reset state
afzal_tahir@yourdomain.com... Using cached ESSMTP connection to smtp01.yourdomain.com. via relay...
>>> MAIL From:<afzalt@nimserver.yourdomain.com> SIZE=5553
250 afzalt@nimserver.yourdomain.com... Sender OK
>>> RCPT To:<afzal_tahir@yourdomain.com>
>>> DATA
250 afzal_tahir@yourdomain.com... Recipient OK
354 Enter message, end with "." on a line by itself
>>> .
250 Message accepted for delivery
afzal_tahir@yourdomain.com... Sent (Message accepted for delivery)
Closing connection to smtp01.yourdomain.com.
>>> QUIT
221 smtp01.yourdomain.com SMTP Service closing transmission channel
root@nimserver(/)#

Check again!
nimserver(/var/spool/mqueue)#ls -ltr
total 0
nimserver(/var/spool/mqueue)#