mailman transport map

[thufir]

I'm trying to follow this guide:

https://help.ubuntu.com/community/Mailman

It calls the postfix-to-mailman.py script when a mail is delivered to a 
list.

Associate the domain lists.example.com to the mailman transport with the 
transport map. Edit the file /etc/postfix/transport:

lists.example.com      mailman:


and am curious as to whether it's a problems that /etc/postfix/transport 
doesn't yet exist.  Should that file get created by a previous step, or 
it makes sense to create this file?  I ask because the wording indicates 
to edit an existing file, and I question how significant that is.


thanks,

Thufir