TNEF
Correlation
Some
messaging systems perform a correlation check on any TNEF stream attached to an
inbound message to verify that the TNEF stream does in fact belong to that
message. This involves matching the value of some field in the header of the
inbound message with a copy of that value stored in some property in the TNEF
stream. Values that are presumably unique for each message, such as message ID
numbers, are typically used for this. The transport or gateway the created the
TNEF stream is responsible for choosing an appropriate value from the message
header and placing a copy into an appropriate property before encoding the
outgoing message s properties into the TNEF stream. Gateways or transports that
receive the message can then extract that property from the TNEF stream and
verify that its value matches the value of the corresponding header field on
the inbound message.
If the values
do not match, the gateway or transport should discard the TNEF stream and
process only the native message envelope. Such checks are prudent because
non-MAPI-based mail clients may attach a file containing a TNEF stream from an
old message to a forwarding or even an unrelated message; if not checked, such
an error may result in the loss of message text.
The header
field value chosen must be unique to the message. There is no fixed header
field for all messaging systems because different messaging systems use
different header fields, but typically the messaging system assigns a unique
identifier to the message which is suitable for this purpose. For example, SMTP
systems typically use the MessageID header, while X.400 systems typically use
the IM_THIS_IPM attribute.