When you attempt to send an X.400 message with an O/R address that has a
null Domain Defined Attributes (DDA) type or DDA value, you may receive a
non-delivery report (NDR) that contains the text "content-type-not-
supported." In addition, an event similar to the following may appear in
the event log:
Source: MSExchangeMTA
Event: 290
Description: A non-delivery report (reason code unable-to-transfer and
diagnostic code content-type-not-supported) is being generated for
message <address>. It was originally destined for <address>;
<recipient>, and was to be redirected to. [MTA DISP:RESULT 16 136] (12)
where <address> is the O/R address and <recipient> is the first recipient
on the message.