opendkim 2.10.3 versus header letter case

From: Kirk MacDonald <>
Date: Tue, 23 Feb 2016 19:12:58 +0000

I’ve been testing a problem a DKIM signer is having using the email relay I administer. To replicate their situation I setup a domain I control for DKIM, setup postfix and opendkim and started testing.

The short version of what I have found is that if I sign using headers like Message-ID or Content-Type, my production relay MTAs (not postfix) seem to be changing these to “Message-Id” and “Content-type”. The actual values of the headers are unchanged.

I used the KeepTemporaryFiles opendkim option to examine what milter is processing and the header names still have the capital letters at that point.

If I specify those headers in the SignHeaders options in opendkim.conf, I get DKIM failures at the recipient side. If I omit them, I get passes. Interestingly I specified the User-Agent header, which my production MTA does not change the letter case of for whatever reason, and naturally got DKIM passes.

Is this letter case changing a red herring, and instead the failures could be “something else”?

Kirk MacDonald
System Administrator

Received on Tue Feb 23 2016 - 19:13:11 PST

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