具有免费许可证的BSD版GyazMail的替代品

• BSD
  所有平台 Windows Mac Linux Chrome OS Android iPhone Apple Watch Android Wear iPad Android Tablet Windows S Web Self-Hosted BSD Xfce Haiku PortableApps.com Slack F-Droid Ruby Gmail GNOME Cloudron Amazon Echo (Alexa Voice Service) OpenPGP PureOS (Purism) S/MIME
• 免费许可证
  任何牌照 免费许可证 开源许可证 商业牌照