As far as I can tell, nobody blocks it. Google sometimes rejects emails where the from address doesn't match the real sending address, which is fair.
I guess the first couple of years were rocky, I hadn't figured out DKIM and SPF and all the other blood rituals yet. Back then I got blocked by Steam and banks. But ever since I set up the correct security it's been fine. Been my primary email for a long long time. All my online accounts are tied to it.
Incidentally, I also have free and unlimited aliases. But I don't usually bother because I have a rule to route all messages to unknown addresses into a special folder. I can give out any random address at my domain and it will always make it back to me. So much more convenient than logging into the website to generate an alias.
The biggest issue was if your ip address got listed in a RBL (Realtime Blackhole List), and then nobody would talk to you. Some were easy to get off, others were permanent blocks, and I found those to be constantly interfering with the delivery of mail. At least the rejection would usually tell you which RBL blocked you.
> Allowed domains are: gmail.com, hotmail.com, yahoo.com, proton.me, protonmail.com, outlook.com, live.com, icloud.com, yandex.com, tutanota.com, tutamail.com, tuta.io
(I’m not saying we should have been doing that, but the company was in insurance and wanted to be extra extra sure.)
But I have only had maybe 3 services ever reject my domain, and those were because the domain contains a number.
I have since stopped doing this out of fear that it will actually cause me more headaches with people/systems that don't understand how email works.
I have never encountered one.
Plenty of providers, but perhaps Apple needs to be forced to open up hide-my-email-providers for others.
Only the EU is capable of doing such thing
