Thanks, that helped a lot. I compared your file to mine and it exactly the same with the exception of the hostname, which is what I would expect.
Yet, I still am not getting the maildirsize files created in the user's folders.
I can only think of two changes I have made to my configuration that are different than the How-To and would not show up in the main.cf file.
I installed Yaa through another tutorial here on How To Forge. That only required adding a table to the mail database.
The other change was that I added a field to both the domain and user tables titled 'enabled'. I then modified the WHERE statement in the Postfix queries to ensure that the account was enabled before accepting mail.
This wouldn't have anything to do with the problem I am experiencing now, would it? I can't see how that would matter, but I don't claim to be an expert on this.