What text encoding is used on MS exchange web server?

Question

Character encoding

Hey!
A response comes from EWS, in which there is a lot of information in such a form, for example:
CQAAABYAAAC16Rcpet5OSKEe9G4bwTmAAABJku2T
I tried to go through base64 and got it
µй)zЮNHЎфnБ9ЂI’н“
. Depending on the change in encodings, the representation changes, but Latin characters and numbers remain in their place. Plus, in one of the answers after base64, the prefix is ​​information in the form of an email address in the Latin alphabet, which is displayed correctly with most major encodings.
mb_detect_encoding insists that it is utf-8, but it is not at all.
Maybe it's not text encoding at all, but something else? Tell me plz!