Alternativer til ZeroMail til Kindle Fire med open source-licens

• Kindle Fire
  Alle platforme Windows Mac Linux Chrome OS Android iPhone Android Wear iPad Android Tablet Kindle Fire Windows S Web Self-Hosted Software as a Service (SaaS) PHP Windows Mobile Java Mobile S60 Android TV Chrome OpenPGP S/MIME DAVdroid
• Open Source-licens
  Enhver licens Gratis licens Open Source-licens Kommerciel licens