Q:

How do I know if Postfix has MySQL/PostgreSQL support?

I'm not sure if my Postfix installation has MySQL or PostgreSQL support. How do I find out?

A:

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!
Run postconf -m:
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 postfix-mysql and postfix-pgsql.

