All of a sudden I started having this problem as well. Over time my queue on this server went from it's normal average of 100 emails at any given time to over 1500 emails in the queue.
I am thinking that several things may cause an error like this. Your problem may not be exactly like mine, but how I went about finding the problem causing my errors may help you find yours.
Here is how I was able to fix mine:
It was not a permission problem.
In an article posted to this group in 1997, someone said that when this error happens Sendmail changes the qf* file to a Qf* file. So, I looked in my mail queue directory and listed all the Qf* files. Then I picked one at random and listed all the files related to that mail id. Basically, I substitued the "Q" with an "*" and it listed the associated df and xf files. I did this to several of them picked at random since there were over 2000 "Qf" files.
By examining these files, we found that sendmail was trying to call up procmail. We had abandoned procmail a long time ago, and had removed the files from the server. Somehow we ended up with a sendmail.cf with procmail references in it. Luckily, I have copies of my good sendmail.cf files, so I put a good one in place and stopped and started sendmail. I also moved all the "Qf*" files and thier assiciated files off the server since they were undeliverable emails anyway.
Within a hour my mailq went from 1500+ to less than 100.
So, look at all the files related to a specific "Qf*" file, specifically the "xf" file since it seems to hold errors for emails that have problems.
Oh! How I found the really old post was to go to
and did a search in the usenet search section. Very cool site!!!
Dave