I'm using sendmail version 8.14.4 on Fedora 15 to send email. My Rails app uses delayed_job to queue up emails. Messages will queue up in /var/spool/mqueue as expected, but don't always get processed. I can see the messages and sendmail is definitely running in the background. Restarting the process does nothing. However, when I issue the sendmail -q command, sendmail gets to work and starts sending. The really odd thing is that this behavior only occurs sometimes. Other times message queue up and are delivered as expected. I've tried tweaking various sendmail configs to reduce the time between queue processing (for example, adding define('confMIN_QUEUE_AGE', '0')dnl to /etc/mail/sendmail.mc), but nothing seems to do the trick. Any ideas what might be the root cause?