OpenDKIM now has enough data to make some interesting observations about
signatures and MIME.
As far as MIME encodings go (only the "outermost" encoding was counted), there
was a pretty common theme:
binary failed 4% of the time
quoted-printable failed 4% of the time
7bit failed 7.7% of the time
base64 failed 7.8% of the time
8bit failed 14% of the time
16bit (?!) never failed (though there was only one attempt)
I expected 8bit to fail more for some reason.
As far as MIME parts go (again, only the "outermost" MIME type was counted),
most of them have about a 90-93% survival rate which is about in line with
general signature survival rates. The one that stands out is
"multipart/signed" (from RFC1847) which drops to about a 65% survival rate. I
don't know much about how this is typically formatted or treated enroute, but
it was easily the biggest outlier in the report. Not sure if that should be a
surprise to us or not.
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