QuickMSG

QuickMSG is a secure messaging format and an Android App of the same name. With it you can send messages either to other contacts directly or to groups. Its aim is to combine the ease of use that messaging apps give with the security of encrypted email.

It is also available in the f-droid app store. (f-droid.org)

There is no central QuickMSG server or infrastructure. Your messages will be sent via the existing SMTP/IMAP E-mail infrastructure. Your messages will be sent using encryption from end to end. Nobody in between can read it. QuickMSG uses well known and established PGP encryption. By default QuickMSG will use 2048 bit RSA encryption for each message. You identify with an email address, not with a phone number. QuickMSG is thus not bound to a phone, but can be used on other device types as well.