ATTENTION:

%%MANPATH%%You should also add %%PREFIX%%/man to your MANPATH (see manpath(1)
%%MANPATH%%or login.conf(5)).
%%MANPATH%%
Do not forget to read http://iain.cx/unix/qmail/mysql.php. After all,
this is NOT our old stock qmail.

You can enable qmail as your default mailer executing:
> %%PREFIX%%/scripts/enable-qmail