There are people who can, every company has them. Usually there are levels, as in "can read number of emails", "can read subjects", up to "can impersonate accounts". Most of the time the mechanism is there for legal reasons. Sometimes people do bad stuff with it.
Normally very very restricted and these days probably requiring security clearance certainly Team leaders on some projects (and not secret squirrel ones) in BT where vetted to TS (Developed Vetting) Level.
Back when I worked in the early days of email (pre internet) on dialcom systems. I had level 6 (SYSAD) on all of Telecom Golds prime's plus Level 7 on the Billing systems and even the BT Security had mandated removal of some of the interesting commands
There where probably 15 or so people in the country that had that level of access
See https://encrypted.google.com/search?hl=en&q=google%20David%2...