A few months ago, I switched from using a Debian based distribution on my main machine to Fedora.
I like to customise my machine a little prior to developing and creating local sites to hack core, create new modules and generally contribute back to the community. Some of the changes are for performance and some of the changes are for vanity. An example of a performance change would be to install PHP-FPM and use it with Apache worker. A vanity change would be to have an ascii Druplicon in my motd; not strictly necessary but pretty cool.
One such change I made recently was to alter the hostname of my laptop since I had not set it on distro install. Unfortately I neglected to map the new hostname to my laptop in either /etc/hosts or /etc/sysconfig/network.
The first realisation
After installing Drupal sites on my local machine I'm accustomed to getting welcome emails. As it happened, I started to not receive any emails. This didn't really strike me as odd or annoying as all they did was serve as a method of speedily filling up my inbox; they were not missed.
However when writing and testing implementations of the subscriptions/notifications modules later on the need to send emails became rather crucial; they were then missed.
Although rather confusing at first I eventually tracked down the missing mails in the maillog where I found a number of messages indicating postfix simply couldn't find the host typhonius-laptop. Rather sheepishly I pinged typhonius-laptop and waited an agonising number of seconds whilst slowly accepting what had happened; 'unknown host'.
Entering my shiny new hostname in my hosts file and a postfix restart fixed everything. So if ever I decide to change hostname and can't send mail immediately afterwards, I'll know what to do, whilst slapping my forehead over and over.