I have this problem.
My email is <catchall>@david.kitchen and for most shops I will give them <shop>@david.kitchen .
Mostly it works.
But when it doesn't work it really doesn't work. And this is OK. If they don't support one of the recent TLDs then I can just fall back to using a throwaway email address. Or if I really need the item I will shop elsewhere :shrug
The annoying edge cases:
1. When <catchall>@david.kitchen works but <shop>@david.kitchen didn't work... like they're actively trying to fight the use of unique email addresses.
2. When <catchall>@david.kitchen works for registration on a web site, but doesn't work for signing in on their mobile app. Because the app enforces different email validation than the website. This is pretty annoying, especially as some apps will put the "change email" functionality in the app... rendering the account useless.
3. When <catchall>@david.kitchen works for registration on a web site, but doesn't work for the payment provider and checkout section. This is by far the most frustrating as you've got so far and are invested in the purchase and now you're stopped. I have contacted vendors about this, it's brain dead.
When email validation fails it's not because they are using a hard-coded list of domains, it's usually because they have a regexp pattern and only consider a 3 letter suffix valid.
I do tell web sites I have this issue, and sometimes they listen. Mostly I take my business elsewhere. Oh well, my choice to have a "difficult" domain name.
Also: People really don't understand email addresses. "What's your email?", "oh it's <shop>@david.kitchen", "If you work for us you're eligible to the staff discount, do you have your ID card?" - This happens, or some confusion of it, more than I would expect.