/tmp: filesystem full

[Cesar Amaya]

Hello list.

I have a question related to sendmail mail.local and /tmp filesystem. 
The issue came out when I started to receive a lot of messages in 
/var/log/messages about /tmp filesystem is full. This is the log from 
system messages:
# tail /var/log/messages
Dec 12 05:48:41 napstats kernel: pid 7240 (mail.local), uid 0 inumber 11 
on /tmp: filesystem full
Dec 12 05:51:31 napstats kernel: pid 7240 (mail.local), uid 0 inumber 11 
on /tmp: filesystem full
Dec 12 06:18:32 napstats kernel: pid 7303 (mail.local), uid 0 inumber 11 
on /tmp: filesystem full
Dec 12 06:21:23 napstats kernel: pid 7303 (mail.local), uid 0 inumber 11 
on /tmp: filesystem full
Dec 12 06:48:45 napstats kernel: pid 7363 (mail.local), uid 0 inumber 11 
on /tmp: filesystem full
Dec 12 06:51:35 napstats kernel: pid 7363 (mail.local), uid 0 inumber 11 
on /tmp: filesystem full
Dec 12 07:19:00 napstats kernel: pid 7426 (mail.local), uid 0 inumber 11 
on /tmp: filesystem full
Dec 12 07:21:50 napstats kernel: pid 7426 (mail.local), uid 0 inumber 11 
on /tmp: filesystem full

But when I run a df -hi it says 0% of capacity is used on /tmp filesystem.

napstats# df -hi
Filesystem     Size    Used   Avail Capacity iused    ifree %iused  
Mounted on
/dev/ad4s1a    989M     76M    834M     8%    1709   139601    1%   /
devfs          1.0K    1.0K      0B   100%       0        0  100%   /dev
/dev/ad4s1e     48G    229M     44G     1%   10600  6560406    0%   /home
/dev/ad4s1d    989M     24K    910M     0%      15   141295    0%   /tmp
/dev/ad8s1d    226G     85G    122G    41%  213086 30357408    1%   /usr
/dev/ad4s1f    171G    8.4G    149G     5%   16560 23205710    0%   /var

from messagess I guess it has something to do with Sendmail. Sometimes I 
run /top /and sendmail is consuming the  most of the processor time.
napstats# uname -a
FreeBSD napstats.americatelsal.com 6.0-RELEASE FreeBSD 6.0-RELEASE #2: 
Thu Mar 30 18:13:14 CST 2006     
root at napstats.americatelsal.com:/usr/src/sys/amd64/compile/NAPSTATS  amd64

I really want to find out what the problem is.
Please can anyone give me some light here?

Thank you in advance.
Regards!!!