I'm not sure if my Postfix installation has MySQL or PostgreSQL support. How do I find out?
The solution is identical to How do i know what postfix is compiled with?, but I guessed you asked in order for the question to be more easily googleable. Clever you!
root@mail:~# postconf -m btree cidr environ hash internal mysql nis pcre proxy regexp sdbm static tcp texthash unix
If you don't have the packages, on Ubuntu, you can install