Features:
- Security you install and forget - SecureEmail will automatically encrypt and sign all outgoing emails and manage the complex certificate exchange procedure
- Full integration with major mail clients - Outlook, Outlook Express, Thunderbird, Incredimail and many other POP, SMTP and IMAP based clients
- Encrypt to anyone, anytime - innovative one-time ´session´ certificates allow you to encrypt email without first exchanging signed mails
- Built-in wizard to lets you quickly download and install Comodo email certificates
- Available in 32 bit and 64 bit versions
- Outlook 2000 and above
- Outlook Express
- Thunderbird
- Windows Mail
- Incredimail
Source: http://www.comodo.com/home/internet-security/secure-email.php