"Turning off Apple's MTA" after postfix port install

[Mark Duling]

The postfix port's ui_msg's say  ".... you may also want to turn off your
system's MTA".  At first I thought I didn't have to do anything because it
worked immediately, but then I discoverd that when sending mail with the
'mail' command locally it was blind to the local aliases.  Here is what I
did to fix that:

sudo mv /usr/sbin/sendmail /usr/sbin/sendmail.old
sudo ln -s /opt/local/sbin/sendmail /usr/sbin/sendmail

Is that disabling the local MTA in its entirety?  Or just a part of it? 
Because I want to change the ui_msg's to be more accurate so people will
know and not spend the time I did figuring out how to make it all work and
I'm not sure if I've done all that should be done.

Mark