What DB would you choose for a (small) virtual server ?

[Frank Bonnet]

Hello

I have to setup a "virtual" postfix server and I wonder what would
be the best / most efficient choice for the DB backend ?
The server will be a small one supporting approx 1000 mailboxes
the machine is a "virtual one" hosted at OVH (France) running Ubuntu 
10.4 LTS
with 4 Gb of dedicated RAM and 50 Gb of disk space.

I've never setup a virtual postfix server so "gurus" advices
would be very welcome.

Thanks a lot