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Re: [ietf-smtp] Survival of arbitrary MIME Content-foo header field?

2018-07-30 12:05:18

On Jul 30, 2018, at 9:53 AM, Dave Crocker <dhc(_at_)dcrocker(_dot_)net> wrote:


If a random -- ie, unknown to the handling systems -- MIME Content-foo header 
field is attached to a body-part, how likely is it to survive, end2end 
transit on the net today?

I'd expect it was very likely to survive, particularly if the MIME was 
well-formed, as intermediate hosts are unlikely to randomly crack open a MIME 
body and rewrite it. That DKIM works remarkably well is a data point there.

The ones I've noticed that rewrite MIME have all been Exchange servers, so 
someone with more Exchange clue might be able to give some insight there.

A few hosts add additional MIME content (advertising, footers), but the ones 
I've paid any attention to seem to do so by fairly crude textual insertion, so 
probably wouldn't corrupt existing content too much.

What if it is at the message header level?  Any better/worse?

That I'm less sure about. I'd expect it to be at best the same or more likely 
worse, as lots of intermediate hosts do look at and modify the headers.



Dave Crocker
Brandenburg InternetWorking

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