East German (ddr) Deutsches Post
This hat should be for German Postal Service as reported in many web sites
In the book authored by Wilhelm Zoller entitled "KOPFBEDECKUNGEN militarisch uniformierter Organisationen in Europa DEUTSCHE DEMODRATISCHE REPUBLIK 1945-1990" it is reported as a later version Wasserwirtschaft but in this book it has a different cap cord
COLOR: gray blue.
CAPCORD: Gold and blue