Cross-platform Email Setup

Recently I switched back to Android after being held up in the Apple ecosystem for the past years. Since iOS 11 the performance (especially battery life) just hasn't been what I expected it to be. At least not on my iPhone 6s. So before setting off for my winter retreat in Thailand, I got a OnePlus 5t. Especially the dual sim option is great for traveling: I can have a local Thai sim card for mobile data, but I don't have to hand out a new number to clients to get in touch with me. All calls and messages to my German number still go through to my phone (even if I probably won't answer them).

Using an iPhone and a MacBook together is a great user experience; from simple things like AirDrop to having a lot of apps on iOS and macOS which just work together seamlessly. (It's the main reason that has been holding me back from switching for over a year now).

My go-to email app has been Airmail for a while now; it's customizable enough but also just get's the job done. Email accounts added on the Mac version are also added to iOS via iCloud. Smart folders is an especially handy feature to keep on top of a topic. Not that other mail apps don't have these features; I just hadn't been thinking about my mail app at all for the past years. After the switch to Android I did. I have installed many apps on my phone now, but none of them is doing what I want them to do.

Airmail has a neat to-do feature: in my setup that's three buttons at the top of each email: To-Do, Done, and Memo. These only apply labels to an email, and I mapped To-Do to a swipe action on my iPhone to quickly flag emails for later.

I haven't found a single mobile mail app that lets me map a swipe (or button) action to a custom label. Apps like VMWare Boxer implement their own to-do feature, which adds more labels to your account. Unfortunately, none of them are customizable and just won't work with other apps.

So for the moment, I am stuck with not having that feature as Airmail does not support default flags/stars. How do you handle email cross-platform? If you have an efficient setup, please let me know.