> A big part of why I’m stuck on/with gmail is that filtering redirects about 90% of those to spam.

That doesn't really make sense? If you used an address on your own domain, other people would be pretty unlikely to enter that email address instead of their own. The problem with misaddressed email should be limited to domains with really high username density; nobody else than the Gmails and Outlooks of the world need to solve the problem because nobody else also has the problem.

Becaus having used an address personally and professionally for close to 20 years, I can’t really abandon it, and I honestly get way too much important stuff to only go I. There once a month or so. If I forward all emails to the new address, I get buried under the avalanche.

Why limit yourself to only either forwarding emails or to "check for important emails" once per month?

For example, email clients generally allow you to use multiple accounts at the same time. Configure your client to read emails from both accounts at the same time, and any time an important email arrives at the legacy account try to update the sender.

(I mean, I'm sure that xkcd.com/1172 applies, but still this seems like an odd thing to be blocked by.)

Becaus I don’t care enough, really. Email is something I use because one is expected to( not because one wants to.

IMHO, that sounds like more effort than configuring Emacs to map a CPU temperature rise to a Ctrl keypress.

I'd rather begrudgingly keep taking advantage of Google's spam filter over adopting the added workflow branch that is perceivably likely to trail me for another decade-plus.

Ha, I knew it was gonna be the workflow one!

Transactional email intended for other people is exactly my problem.

My name is common in certain areas, and I consistently get transactional email from banks, telecoms, and insurance companies around the world.

These businesses do not verify that their customer’s email is truly their own prior to sending emails.

Framing custom domains as the solution to this problem is a bit rash, no?

I'm not framing it as a general solution. But the GP was already migrating to a different domain and claimed this was the main blocker.

Custom domains aren't a panacea, I own my last name as an email domain, but my last name is one letter different from a building supply company in my country . I regularly get purchase orders sent to me instead of them, so even in a small country with a custom domain you can't escape misaddressed email