Hi all! I know that I personally can see the use for a "light" backend. I work for an ISP, and we're implementing dbmail. For that installation with thousands of users and gigabytes of maildata, of course we want to use a midweight contender for our database so we chose postgresql. But for my personal domain, which only handles about 50 users and a few hundred messages a day, this sounds like a good solution. And I still want to use dbmail rather than mailspool just because I like the management and ease of use of it (using our weDBmail front end at http://wedbmail.dsp-services.com/ PLUG PLUG!). Currently using mysql (no innodb), but I can see using a lighter database since that's all it does is dbmail.
Just my not-in-the-least-bit-humble opinion dave -- Dave Logan "Free your mind and your ass will follow." -- George Clinton