Sendmail problems are like Glenn Close in Fatal Attraction. You have to kill them a couple of times just to make sure they're really dead.
I returned home after the jaunty 1,104-mile drive from Dallas to find this server with an 100 percent full disk, which was 70 percent more than the day before. The culprit was Sendmail, which bounced the same e-mail back and forth until it filled the disk.
I burned a Saturday at the keyboard as feeling slowly returned to my butt cheeks -- one of these days, I'm afraid I will break one by driving for hundreds of miles.
Solving a problem with no available disk space takes hours. Commands can take 10 minutes or more to execute, because the CPU's throttled by the process filling the disk. I began by killing the most likely cause, Sendmail: /etc/rc.d/init.d/sendmail stop.
Although I've been running a Linux box for years, I know little about Sendmail, which I regard charitably as the worst software that will ever be written in any language, open source or commercial, under any programming methodology on any operating system. Unlike Apache, MySQL, and other programs on which I rely, Sendmail can't easily be reconfigured. The software's configuration file is so complex that it requires a configuration file of its own!
When Sendmail sends a message, the e-mail ends up in two files in /var/spool/clientmqueue. I deleted each 100+ megabyte e-mail as it showed up, rebooting Sendmail and the server several times, but it took 24 hours to stop coming back.
Like all Sendmail problems that I fix, I was left with absolutely no knowledge of what I did that worked. My best guess is that I could prevent a recurrence if there's a way to tell Sendmail to reject all incoming or outgoing e-mail larger than a set size, such as 10 megabytes.