We have built out some of the things you said were missing for our email system at SmartSurvey. The biggest annoyance is random blacklisting from email provider

We have built out some of the things you said were missing for our email system at SmartSurvey. The biggest annoyance is random blacklisting from email providers. Mimecast almost always greylists us, which is annoying because it creates an artificial baclog on our mail servers, others work fine and then all of a sudden they block you - sometimes you can contact them, sometimes you can't. We also have a big problem with automated tools like mimecast or Office365 because customers don't receive emails that were blocked by some rule or heuristic or other but they just contact us because they can't see what their receiving system has done. Even when we show them the logs. Our sysem sends out about 50 different types of email and some are easy to handle when they bounce, others are not so easy so it will be interesting to see whether your use of webhooks will make things that much better than e.g. MailJet (who we use for some emails) since all of email failures arrive via webhook. Other problem is to do with IP ranges of the sending servers. Using SES probably mitigates some of that (I assume most providers whitelist SES) but if you ever wanted to move to your own hosts, without a /16 subnet, you can easily get blacklisted (again for unknown reasons) and without enough servers to move to, your deliverability suffers. I think the one thing that would help us if we were using a third-party system would be failure messages with specific links to solutions that could be displayed to the end user. e.g. MimeCast 5.7.2 could link to an article about giving permissions to access a Mimecast mailing list. That would save a lot of explaining since we would just show that message to the customer.