A Twitter/X user called @NorCleor has posted the following, garnering over 11 million views within a short period of time:

I cannot imagine any Melbourne Jews (or any Jews for that matter) would write such a letter, but I understand this alone is not a convincing argument. So let’s consider some other indications it is almost certainly fake.
Melbourne’s northern suburbs is not an area where many Jews live
Not many Jews live in the northern suburbs of Melbourne. And it’s even less than it used to be due to current levels of antisemitism. So it is unlikely “there are a lot of Jewish families” in the area the tweeter claims they live. Not that this alone would preclude the possibility of a Jew writing this note, since they could always have lied, but read on.
The author of the note has very poor grammar
The note contains some glaring grammatical errors that make it unlikely to have been written by an Australian Jew: “family’s” instead of “families”, and “live” instead of “living.” Again, it is not definitive proof this is fact, but another indication it likely is.
Where’s the pin or tape?
As journalist Andy Ngo writes: I’ve done a lot of reporting on hate crime hoaxes, particularly by Muslims. This has the hallmarks of one, though instead of a backward or distorted swastika, the symbol is instead a star of David. What part of the note had the pin, tape or whatever was used to hang it on your property? This looks like it was photographed after being ripped out of a notebook.
No Jew drew that Star of David
Whoever drew the Star of David at the top of the note looks like they had trouble doing so, even after practicing it.
The poster is a raging antisemite and terror supporter
As tweeter Drew Pavlou noted:
I am now absolutely convinced this is a fake.
— Drew Pavlou 🇦🇺🇺🇦🇹🇼 (@DrewPavlou) May 26, 2024
I went through her Twitter like history. She’s liked Tweets claiming Jews are natural child killers; tweets by neo-Nazis defending Hitler; denying the October 7 massacre; denouncing non-Muslim Somali’s as “Kafir”. https://t.co/bpN3BRaEtG pic.twitter.com/6Urmyjb3cQ
I would add she has also retweeted Neo Nazi Ryan Dawson:

In other words, someone with an ulterior motive in posting something to stoke more hatred against Jewish people.