S/MIME is described as '(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' and is an app in the Security & Privacy category. There are 2 alternatives to S/MIME for a variety of platforms, including iPad, iPhone, Linux, Mac and Online / Web-based. The best alternative is OpenPGP, which is both free and Open Source.
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 .
With governments and corporations increasingly infringing upon our privacy, we must take steps to protect our private communications and files. With OpenPGP encryption, you can secure your messages and files to ensure that only the intended recipients are able to read them.