Alternativas ao SignMyEmails para todas as plataformas com licença comercial

• Todas as plataformas
  Todas as plataformas Windows Mac Linux Chrome OS Android iPhone Windows Phone iPad Android Tablet Windows S Web Firefox Windows Mobile Microsoft Office Outlook Chrome Thunderbird Mailbird Apple Mail Microsoft Office 365 Outlook Gmail
• Licença comercial
  Qualquer licença Licença gratuita Licença Open Source Licença comercial