@x they have a strict criteria. I tested Migadu against it and it failed for a few reasons:

- Doesn't support DANE
- No valid MTA-STS and TLS-RPT policy
- googletagmanager.com is present on the homepage

I still use them, and have contacted them about these issues, though they haven't gotten back.

They used to list Runbox, though it was removed after they changed the criteria.