Source? Anecdotally many people do. It's actually quite good imo considering the native GUI and features like hide-my-email.

I do, and I am happy with it. I don’t use the Web interface very often but it does the job just fine when I need it. It certainly does not have many features Gmail has, though. Some bits of iCloud are wonky but email works just fine.

I've been using iCloud since they announced support for custom domains. You can have up to 5 custom domains, catch all and 3 aliases for each domain as low as $0.99/mo

First time I hear about them having custom domains, interesting.