I did hear back from the author. The problem was that I was using db3 and the docs clearly state that db4.1 or newer is required. I looked through the Makefile for the p5-BerkeleyDB port, and used the option to build it with db4.1 ... all works great now.

I appreciate your input, but the real reason I asked was to gain a better understanding of perl. Usually I'm able to read through source code and figure things out like this, but in this case I was totally lost, and I susped it has something to do with my understanding of perl not being good enough. I simply don't understand how that constant is ever getting set.

Ah I thought as much.. ;-) ( I mean that it was a DB version issue, not Perl or modules)

The constants.h file in the BerkeleyDB source references the functions; when you build the module, you end up with a shared library, BerkeleyDB.so -- once postgrey invokes BerkeleyDB,

use BerkeleyDB;
[download]

you've got access to all the functions..