Who are your main customer segments? I ask because I'm implementing Microsoft, Google and Apple email support for my app and Microsoft and Google have an API now, while Apple is still a pain. Beyond that, for custom email providers, I'm not sure who else is major enough to implement for. I guess I'm asking, couldn't your customer do something like I'm doing, to cover 80% of the use cases by using the Microsoft and Google APIs and spending some time using an IMAP client for Apple iCloud, and discarding the other smaller percentage of other email providers?
Granted, it still does kind of suck to implement even these three, but I'm sure it would likely suck less if I were part of a bigger enterprise who could afford Nylas for example, which I looked into but seemed too enterprisey for my needs.
