To be honest, we did consider early on checking for this support using the test mailboxes, but that in itself presents issues, seeing as at times you register on a website that has the domain "test.com", but the e-mail arrives at your mailbox from "example.com". This happened quite a few times, actually. Other websites just don't send confirmation messages even when you directly interact with their forms. This seemed really inconsistent to track across a dataset of 1.000 entries, so the idea was dropped.
I understand that it was out of scope for what you did, and I agree that getting sites to send you stuff can be a pain. But if we really want to know whether web sites support EAI addresses, it's what we have to do. Ship this one, now we know what we have to do next time. It'll be more work and cost more but UASG certainly has the money. Regards, John Levine, john.levine@standcore.com Standcore LLC