Alternativas ao ZeroMail para Software as a Service (SaaS) com licença de código aberto

• Software as a Service (SaaS)
  Todas as plataformas 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
• Licença Open Source
  Qualquer licença Licença gratuita Licença Open Source Licença comercial