Kabbalah

In Shu"t Mei'ein Omer pg 274 (not sure what volume, but it isn't volume 6, 7 or 8), a close student of Rav Ovadiah Yosef reports that a man once asked him if he needs to destroy a building he bought because it used to contain a synagogue of Dor De'im, a sect of Temani Jews who stick to strict Maimonidian philosophy and practice, and reject most if not all of Kabbalah. Rav Ovadiah Yosef responded that אי אפשר לדונם ככופרים it is not possible to judge them as heretics.

Welcome to MiYodeya. Here is the standard view of Kabbalah as understood by most Orthodox Jews.

Judaism is a divine religion: it was taught to us by an All-Knowing G-d far beyond our comprehension. When G-d created the world and wrote the Torah, he obviously did so in ways we cannot begin to fathom. However, we can understand a little bit beyond the plain appearance of reality and the plain understanding of Torah.

G-d revealed as much as a human could possibly understand to Moses, and he passed on that understanding to a select few disciples. They in turn passed on these teachings to a few select disciples. These teachings are commonly referred to by two names:

Kabbalah/Tradition: Because these matters can only be understood by transmission.

Torahs HaNistar/ The Torah of the Concealed: Because these matters relate to metaphysical concepts that are not tangible, and deeper meanings of verses beyond the surface meaning.

These teachings are not separate from Judaism, rather they are a deeper level of understanding. This leads to two corollaries:

1. The Kabbalah does not contradict Judaism in any fundamental ways.
2. Only one who has mastered the "revealed" part of Judaism is qualified to study it.

Because Kabbalah deals with matters that are by definition intangible, it must borrow terms such as "world", "light", "flow", etc. to simulate concepts that are beyond our perception. In truth it is highly abstract, and many people struggle with the books written by non-Kabbalists to explain these matters a little bit. This has also meant that people without the correct background misunderstand Kabbalah and thus see it as heretical (I saw the answer on the Christianity SE that is a classic of that "genre.")

Unfortunately, the vacuum of understanding has created attempts by many to "explain" Kabbalah without the proper background. Some people are well meaning, but some are outright charlatans trying to get rich off people's naivete.

The false Messiah Shabsai Tzvi misused Kabbalistic concepts to justify his fake claims and flagrantly transgress the Torah. That created a strong backlash to teaching Kabbalah to the masses that persists to this day.

Anyone who opens a "Kabbalah Center" or claims to teach Kabbalah to the masses is outside mainstream Judaism and not to be trusted. Especially anyone who attempts to use Kabbalah to raise money.

Anyone who treats Kabbalah as a separate religion from Judaism is not legitimate. Anyone who says that Kabbalah denies the existence of Satan or sin is flat-out wrong as wrong can be. (Although the Jewish -and therefore Kabbalistic- view of Satan is very different from the Christian/pagan dualist view.)

One last detail: Originally, Kabbalah was transmitted by word of mouth, as was the rest of the Oral Torah. Some parts of the Written Torah also contain Kabbalistic concepts, such as the visions opening the book of Ezekiel. As the Oral Torah began to be written down, so was the Kabbalah.