It appears that Mauro De Gennaro <[email protected]> said: >Hi all, > >I went through spec-06, bcp-01 and dns-00 looking for anything about header >size limits in bytes and found nothing. BCP 7.5 covers the >number of Message-Instance and DKIM2-Signature fields; I'm not trying to >reopen the discussion about a ceiling on that number, but the >size of those fields is the other half of the same problem and fits naturally >in that section. Spec section 16 is still TBA. The only >place the topic shows up is section 4.3.1 of >draft-moccia-dkim2-deployment-profile, which the WG decided not to adopt, so >I'm not building >on it, and I'm not proposing anything about the recipe or JSON design either. >This is a small operator note for the BCP, with proposed >text further down. > >I think this deserves a few paragraphs because receivers fail in three >different ways when the header section gets too big. Some reject >during the SMTP transaction, which is fine because the sender finds out. Some >drop the connection. Others truncate silently, and for us >that is the bad case. Every DKIM2-Signature covers all Message-Instance and >DKIM2-Signature fields, so a single truncated field breaks >every signature on the message, and the verifier reports "Message-Instance m=x >contains invalid JSON" against a Reviser whose message was >well formed when it left. > >I asked Claude to research what are the header limits defaults on different >MTAs, message stores and cloud providers, details are below. >"Total" is the whole header section, "per header" is one logical field. > >- Sendmail 8.18: MaxHeadersLength 32768 total, 552 5.6.0 [1]
That's just the default which you can override in your config file. I don't see any reason to assume that the other numbers are meaningful, either. In any event I agree with Richard that even 32K is a lot of headers and it's not likely to be a problem unless people are deleting large executable attacchments and trying to describe that in the diffs which serves them right. R's, John _______________________________________________ Ietf-dkim mailing list -- [email protected] To unsubscribe send an email to [email protected]
