GnuPG allows to encrypt and sign your data and communication, features a versatile key management system as well as access modules for all kinds of public key directories. GnuPG, also known as GPG, is a command line tool with features for easy integration with other applications.
- - GnuPG is the most popular Mac & Linux alternative to iPGMail.
- - GnuPG is the most popular Open Source & free alternative to iPGMail.
OpenPGP is the most widely used email encryption standard. It is defined by the OpenPGP Working Group of the Internet Engineering Task Force (IETF) as a Proposed Standard in RFC 4880. OpenPGP was originally derived from the .
- - OpenPGP is the most popular Web-based, Windows, Android, iPhone, iPad, Android Tablet & Self-Hosted alternative to iPGMail.
S/MIME (Secure/Multipurpose Internet Mail Extensions) is a standard for public key encryption and signing of MIME data. S/MIME is on an IETF standards track and defined in a number of documents, most importantly RFCs 3369, 3370, 3850 and 3851.