@doghouse2 I traced it back to an issue with AWS a while back (last spring, maybe), which seems to be what Roku uses to send those messages, and posted an analysis. I'd attribute it more to lack of competence from whatever programming team they used, not malicious intent and certainly not a gmail bias. They may not have the in-house resources to understand the problem and fix it, their expertise is streamers and not email and webby stuff. The flailing around with changing DNS servers (huh? What does that have to do with anything, they should all do lookups exactly the same) and the stock try this reply kind of points you in that direction too. If I wasn't so stubborn I would have returned the Roku TV (our 6th if you count a Roku 3), more effort that it was worth for a guestroom, and I no longer remember what actually made it work. It took about a week of back and forth, including a call from Roku (they tried hard but it was beyond them), until I finally stumbled on a solution.
I'd blame outsourcing to the cheapest vendor, but that's personal bias. On top of that I'd add in poorly done spam detection, probably by AWS, spam detectors often have block lists of email domains that are poorly maintained and updated. I'm retired and didn't bother to figure out how the AWS email sending works or exactly where it was being blocked. No reason to spam check activation requests on previously authorized accounts, that's just plain silly. If they're worried about DDOS type attacks (again, why? there are easier ways to lose friends and uninfluence people) then rate limiting is much better than these outbound email address checks.
A long time ago I dealt with email spam blocking. It's not as easy as it looks at first glance, and it doesn't look like they (meaning the probably contract programmers) even bothered going that far.
Edit: Found it in an old post. I capitalized the domain name in my email, whoever@DOMAIN.COM, to make it work. Email domains are case insensitive, domain.com, DoMaIn.CoM, etc are all treated the same way. Means the problem is pretty brain dead and not very effective if it's purpose was blocking spam.