As lancaster wrote, your rifle was made for Brenneke by Schmidt & Habermann, Suhl. tm ESHA, like all pre-war "Original Wilhelm Brenneke, Leipzig" bolt action rifles. ESHA built the rifle to Brenneke's order on a WW1 Kar 98AZ "carbine" small ring action, as shown by the shape of the recoil lug. The rifle was proofed 1032 = October 1932. ESHA incorporated several Brenneke design features: The closed, welded up "thumbhole" of the left receiver wall (Mauser made such actions only later, after Brenneke made this feature popular), the DRGM protected bolt handle lock with a plunger riding on the extractor and the unusual magazine cover lock. Schmidt & Habermann was a major Suhl gunmaker. As they were predominantly gunmakers to the trade, the name is relatively unknown, as their guns are most often marked by other gunmakers, "name" ones like Brenneke or Barilla as well as countless country gunmakers.
Even if you don't find the small "esha" Schmidt & Habermann, Suhl, trademark in a hidden place on the "Original Wilhelm Brenneke, Leipzig" rifles, the distinctive rear sight base with the ESHA serial number is a giveaway. Here are some photos of such rear sight bases and ESHA numbers: # 38695 and 40764 (with the GS mark too. Opened up to 7x57 and reproofed February 1965) are on Schmidt & Habermann M21 short, small ring actions. # 39299 and 41750 are on "Original Wilhelm Brenneke, Leipzig" rifles, as is 42921 on your rifle. (BTW, my Schmidt & Habermann o/u combination in 16 and 9.2x53R Swiss is # 41481 and proofed in 7/27 = July 1927.)