I host my own email. I also have a gmail account, that I've had since the beta.
I cannot tell you how many times I have encountered a person that asks for my email and then looked at me confused when it didn't end in gmail, outlook, or something, and then ask me for another email, as if only that would be good enough.
I wanted to take a look at Boomi.com but couldn't sign up with gmail, turned on email forwarding for a parked domain to get past it. Stupid behaviour if you are trying to sell a product.
I own my own domain in the .us TLD, and I've been using it for my email for the past 20 years. When I applied for an "Electronic Travel Authorisation" (ETA) to enter Great Britain earlier this year the app flat-out rejected my email address as invalid.
Usually, when that sort of thing happens, I just choose to take my business elsewhere or use my time in a different way. However it really ups the ante when a nation-state refuses entry based on that category of technical incompetence.
I have my own domain and my email ends with a .casa TLD and it not only causes confusion, I have had some websites reject it as invalid.