As a followup to my presentation where I mentioned SMTP line length limits biting me (one of the last slides):
RFC5322 Internet Message Format https://www.rfc-editor.org/rfc/rfc5322.txt
"There are two limits that this standard places on the number of characters in a line. Each line of characters MUST be no more than 998 characters, and SHOULD be no more than 78 characters, excluding the CRLF."
I was slightly off, I said 1024 chars max. It's 1000 hard max, and "aim for" 80 chars max -- including the obligatory CR/LF.
So the fogeys hard-NL'ing their text-only emails... you're doing it right and those young'ns are out of spec! :-)
I still don't know why opendkim was barfing on ~500 char lines. One would think they would allow up to RFC5322 spec. Maybe DKIM spec or opendkim itself has a lower limit. I tried using the source luke but I couldn't quickly find the offending code, and since my bug was solved, I moved on.
Upon further reflection, perhaps I should file a bug...
Now, to go and make sure my custom headers are wrapping at 76...