The letter is in the Federal Archive/BDC, personal file of Walter Foehl, and is quoted on page 135 of the book "Architects of Annihilation", by the German leftist historian Goetz Aly.Every day we have trains coming in with more than 1,000 Jews a time from all over Europe. The medics patch them up, and we either house them here temporarily or mostly ship them on into the Ukrainian marshes, in the general direction of the Arctic Ocean, where - assuming they survive (which the Jews from the Kurfuerstendamm or Vienna or Bratislava ertainly won't!) - they are all being collected together to await the end of the war, though not without having built a few autobahns in the meantime. (But we're not supposed to talk about that!)
Aly points out that the language used in the letter contains clear echoes of the minutes of the Wannsee Conference. The words in the minutes that Aly refers to are "....the able-bodied Jews will be taken off to build roads in these territories, where large numbers will undoubtedly be lost through natural wastage".
One might wonder about the reference to the arriving Jews being patched up by the medics. That could possibly be a hint at a process of selection by German doctors, with those assessed as fit for labour being sent onward into Ukraine to be used for road-building, as Foehl states.
His reference to "Housing them here temporarily" might possibly be a hint at the killing of those assessed as unfit for labour, but that can only be a conjecture. The literal sense of the letter suggests the concentration of the Jews in transit camps awaiting despatch to the "Ukrainian marshes", perhaps after undergoing a selection process.
Whatever the case may be, this letter is a piece of documentary evidence from a senior official in the Generalgouvernement indicating that at least some of the Jews deported there were sent further into the Occupied Eastern Territories for use as forced labour.