Enigmail
Requires GnuPG to be installed.
Pretty Easy privacy (p≡p) in development to make encryption more user friendly.
Tightly integrated suport for OpenPGP with Mozilla Thunderbird and Mozilla Seamonkey (and other Mozilla-based mail clients)
Encrypt/sign mail when sending, decrypt/authenticate received mail
Support for inline-PGP (RFC 4880) and PGP/MIME (RFC 3156)
Per-Identity based encryption and signing defaults
Per-Recipient rules for automated key selection, and enabling/disabling encryption and signing
Integrated OpenPGP key management user interface
Automatically encrypt or sign attachments for inline PGP messages
Powerful GUI for easy configuration and OpenPGP key management
Detailed user preferences for advanced configuration
Integrated OpenPGP PhotoID viewer
Supports OpenPGP key retrieval via proxy servers
Integrates with GnuPG, versions 1.4.x and 2.x
Supports Mozilla's Multiple Identities feature
Official release available for: Windows, Mac OS X, Linux x86-32 and x86-64 (all in one release file)
Contributed / distribution builds for other operating systems such as Linux, Solaris, *BSD and OS/2
Many Language Packs, (mostly) included in the official releases, and available separately for localisation of contributed builds.
Save passwords - Remember password for ... minutes idle time: Determine for how long your GnuPG password should be kept in memory if you don't use Mozilla. This is a certain security trade-off if other people might have access to your computer while you are absent. To disable the password caching, set the value to 0.
Server location - ?
Free - Yes but accepts donations.
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Jumble
Mobile email encryption _ i phone app & "working hard on an Android version".
End-to-end encryption.
Encryption method called AES-256
Plug in for g mail.
"Working hard to bring more platform coverage to our users and we plan to launch Jumble support for Office365 and Outlook for desktop imminently with Yahoo Mail, Hotmail and Outlook.com as soon as possible".
Jumble uses Google Analytics which tracks anonymous website usage only.
Importantly, while Jumble stores users' private keys they are only stored in an encrypted format, accessible only by the users' password which is not known or stored by Jumble.
Store password - No.
Cost - For business & free for personal.
Server location -
Jumble is an Irish registered company and uses (as much as possible) Irish and European infrastructure. Jumble data centres are located in Germany.
As an Irish company Jumble is obligated to deal with requests from the Irish government and legal system; Jumble does not deal with requests issued outside of Irish jurisdiction.
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Mailvelope
Open PGP encryption for webmail.
Mailvelope comes preconfigured to work with the following webmail services:
GMX
WEB.DE
De-Mail
Gmail™
Outlook.com™
Yahoo!Mail™
Using this general approach, it can be configured to work with any webmail provider. You can make these settings in the Preferences section of the Options view.
Mailvelope can cache passwords for private keys in the local memory. You can activate the cache in the security settings or with the password dialog. Passwords have a certain lifetime, which can be adjusted in the settings, and are always deleted when you close the browser window.
Save passwords - Mailvelope does not have a password recovery mechanism. If you forget your password or lose your private key, there is no way to recover any encrypted message.
Cost - Free.
Server location - ?