I recently upgraded the Postfix mail server from 2.3.8 to 2.4.0 on a Debian linux server that has a 2.4 kernel due to other applications that it has. I always check the bug reports before upgrading packages but I obviously missed Debian bug #417530, whose summary is Fatal error: “epoll_create: Function not implemented” using kernel 2.4 and postfix 2.4. Normally Debian’s APT package management system contains all the dependencies but it did not contain a dependency on kernel 2.6 for the new epoll() function, which can improve network socket performance.
After upgrading Postfix I tried sending an email but Thunderbird gave an error message so I checked the syslog on the server and discovered the that the /var/log/syslog contained the following error message: postfix/master[24312]: fatal: epoll_create: Function not implemented I searched for Postfix bugs using the Debian bugs by package search plugin for Firefox.