What is this …. (FYDIBOHF23SPDLT)

You may notice that the Legacy Exchange DN value in onprem AD typically contains something like :

ou=External (FYDIBOHF23SPDLT)/cn=Recipients

Just in case you were curious, the FYDIBOHF23SPDLT value is a constant, it’s basically the phrase EXCHANGE12ROCKS…  the letters are all alpha-shifted one character.

It’s changed for each version of Exchange over the years.

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