Simple API, Complex Emails (Jakarta Mail smtp wrapper)

A S/MIME library for JavaMail

Spongy Castle - a repackage of Bouncy Castle for Android (which ships a crippled version of BC)

Java Email Send Client with support for DKIM, S/MIME and PGP/GPG

A simple Encryption Mail app that is able to read and send encrypted messages using EAS protocol

A digital signing library for use in Java projects which send email