Magic Earth is not an open source app. They haven’t released any source code. Mentioning it as the OP title is about open source maps app.
https://www.magicearth.com/faq-en/
Will Magic Earth be Open Source?
No; since it is also used commercially (we have a paid Magic Earth SDK for business partners), we cannot make the code public.
That being said, I love using Magic Earth for driving. It works quite well as long as your area is up-to-date on OSM
I personally like both Posteo and mailbox.org, but they are paid email services.
You can use them for your email, contacts, calendars, and tasks. On Android, you can use Davx5 to sync them.