Between posting my question and receiving your reply I found the following information 'on-line':
In 1913 the structure, organization and scope of activity of the military postal system was reorganized in Austria-Hungary as set out in the Dienstbuch E-47. According to
this rulebook, the Imperial and Royal Feldpost was a ‘joint army institution’, the task of which was to convey all official and private post (letters, postcards, printed material,
newspapers, commercial samples and parcels) between the army in the field and the home front.
This seems to indicate that the military feldpost system was an actual Army function prior to the commencement of hostilities in 1914. Were civilian postal staff seconded to the Army to help run the feldpost service prior to the outbreak of war?