I believe it is called a "server printer" because multiple people are hooked up to this printer.
According to my Quick-Reference it is :
Description: ESF =
(1) External Source Format
A data format that makes it possible for VisualGen to
import member definitions developed outside VisualGen. The
format consists of a readable set of tags and attributes.
The external source format is also used to export member
specification library (MSL) members for hard-copy printing,
editing, and analysis.
IIRC the network printer is probably being selected by the class and form. If the printer has not been setup to do portrait there will probably be no way for you to force it. If the printer has been setup to do portrait, then it probably needs another selection criteria such as a different form (or possibly class).
This is the way (again IIRC) that VPS runs. You need to communicate with the people in charge of the printer setup to find out if it is setup and how to get selected for portrait.
Then again, you could always bury (ASCII ?) printer codes in you output and force a switch the way we use to have to do for PC printers...