Last year I was notified by Audi that my email address had been compromised in a data breach. As the spam volume to that mailbox increased, I decided to change it. I discovered that I cannot change the email address associated with my Audi account. When I contacted their Technical Support group, they advised me to delete the whole account (which failed), and create a new one.

As in, they check "if domain != 'gmail.com' { fuckyou(); }"? Or as in "they MTAs are not very good and just don't deliver email"?

I have accounts in the US, EU and Asia due to family, etc. and this kind of restriction is fairly common in EU/Asia

Interesting; I can't say I recall ever encountering such a restriction anywhere, including banks, and I have or had bank accounts in a number of European (and other) countries. I've encountered other problems, but not this. Not that I'm doubting your experience of course; just interesting I never had problems with it.

I do a lot more business in cash locally as a result. Finding a good local bank that will let me physically show up to deal with problems with my money was the hardest part due to the massive consolidation in that industry, but the result is that I am more connected to my community and more resilient to many types of problems.