OpenPGP Mail Clients

The following links to plugins/extensions to add OpenPGP signature support to your current Email program

Many other links to GnuPG plugins

PGP Corporation's PGP Desktop ($$) works with many email programs on Win2000, XP, and Mac OS X. (Probably uses proxying, not plugins)

• Any: Tiger Envelopes

Windows

• Thunderbird: Enigmail
• Mozilla: Enigmail
• Netscape: Enigmail
• MS Outlook: GPGol; an old plugin
• MS Outlook Express: ?
• Novell Groupwise: ?
• Lotus Notes: ?
• Eudora: ?
• Pegasus: ?

Mac

• Mail.app: GPGMail
• Thunderbird: Enigmail
• Mozilla: Enigmail
• Netscape: Enigmail
• Entourage: EntourageGPG
• Eudora: EudoraGPG/
• Mailsmith: Mailsmith-GPG

Linux

• Thunderbird: Enigmail
• Mozilla: Enigmail
• Netscape: Enigmail
• Evolution: ?
• KMail: instructions
• Pine: pinepgp
• Mutt: instructions

Web Mail

• HORDE/IMP: upgrade to server software to IMP 4.0+
• SquirrelMail: G/PGP Encryption Plugin

• Firefox plugin to add S/MIME support to Gmail; could be used as a basis for a browser-based PGP plugin for yahoo/hotmail/etc.
• Greasemonkey should be able to do it too
• GMail - FireGPG (works generically with all textareas)
• Yahoo!Mail
• Live Mail (Hotmail)
• Hushmail.com

Programming Libraries

• Perl: Mail::GPG
• PHP: pgp_mail()
• Python: Use Pyme and Email modules
• Java: PGPMime for Java
  • OpenPGP: The Legion of the Bouncy Castle Cryptix PGP Java API Commons OpenPGP
  • Mail: Commons Email JavaMail