I've heard enough of these horror stories to know it's a real problem, even if only for a relatively small percentage of users it's not acceptable (even more so because of their notorious lackadaisical support/recovery process). That said in the case of OP it seems they didn't do any of the basics steps to improve deliverability, so in that particular case I think pinning the blame entirely on Gmail is a stretch.

Thanks for sharing.

We can't reply to email questions from gmail users asking for an update on our shipping progress, so in this case, the customer is emailing us and we're not able to reply. We've since reverted to calling the customer to respond. Left a voicemail to one this morning and got a text back: "Don't worry take your time".

I don't see them claiming the same happened to Microsoft, Yahoo or other email providers and I know for a fact that all of that stuff has happened to me from mail servers that seemed to be configured just fine.