I don't recall any kind of retention limits at Microsoft, at least not for engineers. My mail archives went all the way back to my hire date even 15 years later.
When I worked at Capital One there was a policy of automatically deleting everything that had not been subpoenaed as soon as it was legal to delete it. Usually 3 years or so. Retaining longer was viewed as creating legal risk for future lawsuits. They didn't want to leave evidence lying around if they could help it.
My company moved to a 3 year retention for legal purposes a few years ago. Somewhat annoying from a nostalgia point of view when I’d get mails pop up from 2095, but everything I need has been in jiras for the last 10 years.
Edit: We were on GSuite.