I would think that the idea behind the MIME delivery failure notification messages is very good. Although there are many English speakers in Germany, many users ask for support because they dont understand the error messages. A MIME delivery status aware mail reader could display things much better than a simple text message can.
However, an implementation like this:
>> To: Alice@???
>> From: postmaster@???
>> Subject: Delivery Notification (failure) for Carol@???
>> Content-Type: multipart/report; report-type=delivery-status;
>> boundary=bcdef
>> MIME-Version: 1.0
>>
>> --bcdef
>> Content-type: text/plain; charset=us-ascii
>>
>> Your message (id QQ314159) could not be delivered to
>> Carol@???.
>>
>> A transcript of the session follows:
>>
>> (while talking to Ivory.EDU)
>> >>> RCPT TO:<Carol@???> NOTIFY=FAILURE
>> <<< 550 error - no such recipient
>>
>> [...]
is very bad. There should be text before the first MIME boundary, explaining the strange look of the message for non-MIME-aware mail readers. And there should be a more detailed text in the 'text/plain' section.
A transport agent should indeed concentrate on the transport, but it does also send messages (error notifications), and there is no reason not to send them using MIME as far as I see, but there are several reasons to use MIME, such as automation and multi language support etc.
Regards,
Moritz
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