* Overview

This document defines the TNEF file format.

* File Format

(Note: items delimited by '<>' are literal values or descriptions of
the value. All other tokens are defined in the format.

     tnef_stream :: TNEF_SIGNATURE key object

     key :: <nonzero 16 bit integer>

     object :: message_seq
            :: message_seq attach_seq
            :: attach_seq

     message_seq :: att_tnef_version
                 :: att_tnef_version msg_attr_seq
                 :: att_tnef_version att_msg_class
                 :: att_tnef_version att_msg_class msg_attr_seq
                 :: att_msg_class
                 :: att_msg_class msg_attr_seq
                 :: msg_attr_seq

     attr_tnef_version :: LVL_MESSAGE attTNEFVERSION
                          <sizeof(ULONG)> <0x000010000> checksum

     msg_attr_seq :: msg_attr+

     msg_attr :: LVL_MESSAGE attr_id attr_len attr_data checksum

     attr_id :: <one of the defined attributes>

     attr_type :: <one of the defined attribute types>

     attr_len :: <length in bytes of attr data>

     attr_data :: <data associated with the attr, attr_len bytes long>

     attach_seq :: att_rend_data
                :: att_rend_data att_attr_seq

     att_rend_data :: LVL_MESSAGE attATTACHRENDDATA
                      <sizeof(RENDDATA)> renddata checksum

     renddata :: <contents of the RENDDATA structure>

     att_attr_seq :: att_attr+

     att_attr :: LVL_ATTACHMENT attr_id attr_len attr_data checksum

     checksum :: <integer which is the sumb of bytes % 65536>

     TNEF_SIGNATURE :: <0x22e9f78>

     LVL_MESSAGE :: <0x01>

     LVL_ATTACHMENT :: <0x02>

     attTNEFVERSION :: <0x9006>
     
     attATTACHRENDDATA :: <0x9002>


All attribute names are defined in src/tnef-names.data; all attribute
types in src/tnef-types.data.

* Notes on Attributes

This section describes special handling needed for some attributes.

** attATTACHMENT (0x9005)

This attribute has some interesting MAPI properties in it. Most
importantly is the long filename MAPI property. The MAPI proerties
have the following structure:

Property_seq :: <integer property count> Property_value

Property_value :: property_tag Property
               :: property_tag Proptag_name Property

Property :: Value
         :: value_count Value

Value :: value_data
      :: value_size value_data padding
      :: value_size value_IID value_data padding

Proptag_name :: name_guid name_kind name_id
             :: name_guid name_kind name_string_length name_string
                padding

* Data Structure

In some cases the attribute data is structured data. This section
describes those data structures.

** date

     struct date
     {
         int16 year, month, day;
         int16 hour, min, sec;
         int16 dow;
     };

The dow member is zero based with Sunday equal to zero.

** RENDDATA

This data structure is not currently defined since it is unclear that it is
needed by anything other than Microsoft Outlook.