I recently set up a new computer with Ubuntu 11.04 amd64, set up as a desktop. I hadn't got around to setting up an email client to read system mail, and I was curious what unread mail might have built up. I was surprised to find that /var/spool/mail was empty, that /etc/aliases did not exist, and that neither exim4 nor any other mail transfer agent (MTA) was installed.
My previous computer had exim4-light installed, and I had reconfigured it a few times, but I don't remember installing it. I had started with Ubuntu 8.04, and upgraded it in place with each release as they were released, until 11.04. I'm wondering if exim4-light was installed by default with some earlier release of Ubuntu, or if it was installed as a dependency of something else I installed.
(I'm also wondering whether to bother installing an MTA, as perhaps checking routine system mail was a waste of time better spent playing Minecraft, but that's probably a subjective question.)