Thanks to this forum post on sendmail issues, my Linux laptop now actually boots quickly, whereas before it was taking years to boot. Apparently, /etc/hosts has to look like the following for me:

127.0.0.1       localhost.localdomain   autumn

I hadn’t realized the localdomain component was required by sendmail, or else it runs into severe name resolution issues that apparently have very high timeouts.

Now all I have to do is fix this weird DMA hanging problem that I’m having occasionally on boot…