Developer Information about TNEF

• MSDN: Transport Neutral Encapsulation Format
• MSDN: Message Transfer
• MSDN: MAPI Property encoding in TNEF streams
• Digging Deeper into CDO - has a decent list of some of Microsoft's undocumented MAPI properties.
• CDOLive -- A great resource for lists of the undocumented properties. (Thanks Andreas Boeckler)
• The Compressed RTF Format - From the creators of jTNEF, a great document on how Microsoft mutilated another open standard (LZ Compression) for their own use.

Developer Information about other stuff

• Personal Data Interchange
• PDI Developer's Information - Specifications for vCard 2.1 & vCalendar 1.0
• RFC 2445 - Internet Calendaring and Scheduling Core Object Specification (iCalendar)
• RFC 2446 - iCalendar Transport-Independent Interoperability Protocol (iTIP)
• RFC 2447 - iCalendar Message-Based Interoperability Protocol (iMIP)
• RFC 2426 - vCard MIME Directory Profile. (VCard 3.0)

Other TNEF products

• TNEF - simple utility to extract attachments from TNEF streams.
• kTNEF - program similar to TNEF, but with integration with KDE.
• TNEF Clean - a script to run with TNEF and reformat streams in email.
• Fentun - a closed source, cross platform TNEF parser.