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.