@aerion @_elena jep; I did that email-comparison, too (in this talk, recorded in 2024, context: higher education institutions: https://video.notizlab.de/w/aaf8hYURi9JF3VLooSdtbn)
Would be crazy, if you could only send/receive emails from the same provider as you're using. Especially, since many HEI have their own email infrastructure.