Truly modern consumer sensibilities are fascinating to me.

Personally I do not use any Apple or Google products. There are so many better choices!

Anyway, might I suggest services that run standard open source mail daemons that never restrict you, like Migadu.

https://www.fastmail.com/how-to/email-for-your-domain/

Maybe GCP. It's like saying the tiger had no prior history of violence.

I find this sentence confusing. Do you mean “forge” in a technical sense of “this email came from a server unassociated with the domain”? I don’t really get it. I’ve know this feature existed in Gmail for 15+ years and have made regular use of it. Plus I’ve used it to help older relatives keep an old address alive.

how can you "forge" something if you verify ownership? when you own something, it's not "forging" to use it.

i think the point you're trying to get at is that the mail might fail dmarc requirements?

Either way, this is likely going to stop me from using Gmail as my mail aggregator, I've used this feature for nearly a decade to send and receive from 6 different addresses, Gmail recognizes the to address and automatically sets the from address to the correct account.

Is Thunderbird still decent nowadays? What's a decent mobile + desktop replacement?