Gregory's Server
@g right. Let's try this:
A, B and C are people with email addresses.
B has Gmail, A and C do not.
There are nine possible email messages: A to B, A to C, B to A, B to C, C to A, C to B, A to B and C, B to A and C, C to A and B.
Only 2/9 or about 22% don't go through Gmail.
"I see a lot of stuff come through Gmail" is reasonable, but it doesn't mean everybody uses Gmail.
@evan To get the real numbers I guess I could dump a few years of email and parse MX records for domains, but it's safe to say a large portion of it does as your scenario shows.
I think it's not that big of a problem as I never felt like I *had* to have a gmail email account, but I do feel like self-hosting has gotten much worse in the last decade or two due to hard to use software, aggressive spam filtering on the big providers that are biased against small ones etc.