Comment by gus_massa
In the math department, we had a Moodle the students in the first year of my university in Argentina.
When we started like 15 years ago, the emails of the students and TA were evenly split in 30% Gmail, 30% Yahoo!, 30% Hotmail and 10% others (very aproxĂmate numbers).
Now the students have like 80% Gmail, 10% Live/Outlook/Hotmail and 10% others/Yahoo. Some of the TA are much older, so perhaps "only" 50% use Gmail.
The difference is huge. I blame the mandatory gmail account for the cell phone.
Anyway, we had weird problems with Live/Outlook/Hotmail and Yahoo because they classified some of our emails as spam. Gmail usually works better.
Anyway^2, everyone is using WhatsApp, so it doesn't matter.
In what way would you consider WhatsApp a replacement for email? Instant messaging is a completely different use case.