I do not know the answer to this question but I do know that the Gemara Menachos 32b (first line before the wide lines) states that there is a Gezera Shava of "Ketivah Ketivah". Rashi DH Ketivah (in the first pshat) writes that Ketivah is stated by the Torah in connection with Mezuzah and Ketivah is also stated by the Torah in connection with Get. Since there is a Gezera Shava between Mezuzah and Get it maybe that Get and Mezuzah are compared for writing on the backside.

Chodesh Tov

Dovid Bloom

Follow-up reply:

However I do not think that this could be a Halacha, since the Rambam Hilchot Mezuzah 5:4 writes that it is only a custom to write the name "Shakai" on the outside of the Mezuzah.

Dovid Bloom

Hi Chaim,

You are proposing an interesting analogy. As far as I know, you are the first to connect the two, and that in itself is a chidush!

The usual explanation for the writing the names and hints of Hash-m names on the backside of the Mezuzah, has to do with the aggressive stand the Ramabam (Hl. Mezuzah 5;4) against those who added names of angels for Segula reasons. The customary understanding of the Rambam's strong stand, is that he was mainly reffering to those who wrote the names on the inside of the Mezuzah.

In any case, I can just add, that we find some parallelism between Mezuzos and Gitin. There are those who reffered to Gitin as Kodesh regarding the use of the Ashuri font usually used for Sifrei Torah etc. for the Get. BTW, in a Get found in The Cairo Geniza, there was tracks of a custom of writing names of angels in the Get.

Kol Tuv,

Aharon Steiner