It looks like the White House Office of Political Affairs used gwb43.com all of the time.

Click here to enlarge.

I googled "jsj@gwb43.com." And this pdf file comes up. Looks Jennings and two other employees who worked in the WH office of Political Affairs conducted offical business on the gwb43.com account. And of course, Karl Rove was the head of Office of Political Affairs.

On a side note: Jennings was mentioned in an inquiry into the politicization of the General Services Administration.