Normal operation of AI often involves exhilaration of data to the vendor, so I take the privacy qualifiers with a grain of salt. This most likely is turning your email inbox into something roughly as (non)private as a search engine query. It's the ultimate dark pattern, goodness knows what MS intends to do with this access.
Even if it doesn't work right - having it at all is going to result in all sorts of bullshit for employees where this is enabled.
Someone digging through your emails because you happened to mention some vaguely related keywords... yeah, no.