The memorandum, titled "Reflection on the Treatment of Peoples of Alien Races in the East", is certainly genuine.
Though if I understand correctly, what we have is not the memorandum (said to be
6 pages long) itself, but rather Himmler's own summary of it and his further notes to self on dissemination.
These notes were entered as Document No-1880, Prosecution Exhibit 1314 at the Nurenberg military tribunal.
There is a full English translation available on a number of websites. E.g. here.
Apparently, Generalplan Ost was based on the ideas raised by Himmler in his memorandum.
- Most emphatically, Himmler (or other top Nazis) was not against mass murder. On the contrary, by the time the memorandum was written, the Einsatzgruppen had already murdered at least 65,000 Jews (as others have noted in their answers/comments here already).
- However, it does seem to be true that at that stage Himmler (and other top Nazis) did not consider outright mass murder as the only way to "solve" the "Jewish problem". What Himmler writes later on in this document is:
I hope that the concepts of Jews will be completely extinguished
through the possibility of a large emigration of all Jews to Africa or
some other colony.
Again, others have pointed out that what he had in mind was a ghetto writ large, at best. Recall that the official Nazi line was not that Jews were being murdered but rather "resettled in the East". So the Madagascar project might as well have easily morphed into a huge death camp too had it been implemented.
- When context is considered, it becomes clear that the quote about un-German methods was not even referring to Jews. This is the full context:
For the non-German population of the East there must be no higher
school than the four-grade elementary school. [...] Apart from this
school there are to be no schools at all in the East.
from the beginning want to give their children better schooling in the
elementary school as well as later on in a higher school, must take an
application to the Higher SS and Police Leaders. [...]
acknowledge such a child to be as of our blood, the parents will be
notified that the child will be sent to a school in Germany and that
it will permanently remain in Germany.
Cruel and tragic as every individual case may be, this method is still
the mildest and best one if, out of inner conviction, one rejects as
un-German and impossible the Bolshevist method of physical
extermination of a people.
As explained before, these pipe dreams of Himmler are referring to an East already cleared of Jews. So, he is holding forth about the various Slav peoples here and comes to the conclusion that mass-murdering them might not be practical after all, and perhaps not very sporting. Even such a "courtesy" is not extended to the Jews.