TabMail

TabMail for Windows (95/98/Me/NT/2000/XP) is mail user agent (MUA) for sending, receiving and managing your email messages. It's small and fast, conforms Internet Standards and supports Unicode characters.
Some other properties:
* Automatic attachments compression with zlib library
* Warn when open (or save) dangerous attachments
* Message filtering (input and output) using regexp TRE library
* Spam filtering using SpamBayes message header additions
* Simple view of compound messages
* Message-thread can span many mailboxes
* HTML messages view as plain text (see htmlp for more details).
* Easy PGP message encryption/decryption
* SMTP and POP3 authentication
* Support for SSL/TLS connections
* Scanning attachments for viruses
* Multi-user and multi-account
* Tracing for diagnosing TCP, POP3, SMTP or filter errors