mail is not sent, instead just coping into /var/spool/queue dir

Hi,
I have some problems w/ the sendmail. I see that messages are queued in the /var/spool/mqueue
and they are never sent to the recipients. This problem just suddenly started without any modifications in the current configuration. I already started and stop the sendmail and it did not help.
Also, I tryied to set #O QueueLA=22 and #O RefuseLA=20
in the sendmail.cf file, it also did not help.

Thank you.

What error are you getting in /var/log/maillog...

No. I do not see any errors.

• T

I see the following error
mailhost.dbd.com: host name lookup failure

When I try to execute
# /usr/lib/sendmail -q -v

or 

# /usr/lib/sendmail -OQueueLA=100 -q -v