Today I’ve had some serious battles with Dovecot running on a wild cpu time spending spree. I recently made an apt-get upgrade on my Debian system. Somwhere in there things went awkward. An imap process simply wouldn’t stop on /etc/init.d/dovecot stop nor kill -9 [dovecot-pid] The process took 100% cpu and eventually the whole system, including kernel, froze. Had to cold reboot it via IPMI three times! Thank god for IPMI.. Anyways I found this mailing thread with the same issue. What seems to have solved to problem for me was to upgrade Debian from lenny to unstable, including the latest Debian kernel (18.104.22.168-686) and Dovecot 1:1.2.10-1 and keeping my fingers crossed while rebooting. I also noticed some complaints for a missing “cpusieve” plugin. Uncommenting plugin = cmusieve in dovecot.conf was necessary.