[michaelt]

The problem with deliverability issues is the impossibility of proving a negative.

If I send an e-mail to a company's customer support, or to my senator, or I reply to a potential client, or I contact an open source mailing list and I don't receive a reply - do I know if my message made it to them or not?

I mean, it's plausible that [e-mail] just didn't deign to reply to my e-mail. But it's equally plausible there's some subtle misconfiguration - like an e-mail forwarder that breaks the SPF signature. It's not like I can sign up for a senate.gov e-mail address to test with.

Meanwhile, to paraphrase an old joke, when your senator rejects your e-mails you have a problem. When your senator rejects @gmail.com they have a problem.

[defanor]

Sure, strictly speaking it's impossible to ensure that a message was actually read by a user even with automated end-to-end delivery acknowledgements and/or in centralized systems: UIs manage to gobble/hide messages, users fail to find how to open attached documents (and declare that those are missing), etc. But I imagine that a survey/statistics would still help to estimate how bad deliverability in general (in a variety of common cases) is: without that there are differing and even more vague ideas of its state.

[noduerme]

I can prove a different negative with my own mailserver - when I've sent things to @gov, they've always been responded to. I think that just proves the government reads ALL their spam.