Postfix cannot do what qmail can do. Specifically, users can create and destroy email addresses themselves with .qmail files. This is different and more powerful than Google's plus-addressing approach. There are many, many other features of qmail's implementation that Postfix cannot compete with.
Postfix is not alone in this; no other MTA/MDA can do what qmail can do.
Postfix is not alone in this; no other MTA/MDA can do what qmail can do.