Beta version 2.0 was released and it has this bug fixed.
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https://plus.google.com/communities/102581534035171613663Arnaud Lejeune commented
I'm not sure the fix is working: I do have a Nexus 5 with Android 5.0.1 - Boxer 1.4.10, and I can't add my gmail account for Boxer.
After I authenticated and I gave Boxer the authorizations, I had the message: "Impossible de contacter le serveur" (Can't connect to the server). Then, I am sent back to the welcome screen.