Path: csiph.com!eternal-september.org!feeder.eternal-september.org!.POSTED!not-for-mail From: "Helmut K. C. Tessarek" Newsgroups: comp.mail.sendmail Subject: autoconvert messes up DKIM signature Date: Fri, 31 Oct 2025 17:21:17 -0400 Organization: A noiseless patient Spider Lines: 41 Message-ID: <10e398f$qf2r$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Fri, 31 Oct 2025 21:21:20 +0000 (UTC) Injection-Info: dont-email.me; posting-host="e4d774d0b461f7a38889962e8a028f22"; logging-data="867419"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+39yFgYcLJjnKe4Uqi1fQD" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:h3s542Tn4sgXrMtDPpdqrWU+kfo= Content-Language: en-US Xref: csiph.com comp.mail.sendmail:8196 Hello sendmail experts! Today I sent myself a test email from an updated k9-mail client and imagine my surprise as the DKIM check failed with "Invalid (E-mail was modified)". I checked the mail headers and found the following: X-MIME-Autoconverted: from quoted-printable to 8bit by [bla] 59VKaHmW832917 Weird, why would sendmail do such a conversion? I never told it to do so (or at least I think I never did). I guess k9-mail sent the mail in a format sendmail didn't like. However, there is nothing I can do about that. But what is even weirder is that sendmail modifies a signed email. So this basically breaks DKIM. This brought a few interesting questions to light, some of which most likely show my non-sendmail-expert status. So please bear with me: 1. Why would sendmail modify the mail after it was signed? Is there a way that sendmail does this conversion before the opendkim milter signs it? I can't be the only one who uses opendkim and sendmail. Modifying an email after is was signed clearly makes no sense. 2. Is there a reason for sendmail to do this conversion in the first place? Afaik quoted-printable is not an exotic/unknown format and thus should be understood by today's clients. 3. How can I turn off this auto-conversion? Would it result in drawbacks? While the 3rd one is the brutal approach, I'd rather go with the 1st one, which also makes the most sense in terms of a mail processing workflow. Unfortunately I don't know how to do either. Here is my sendmail.mc: https://evermeet.cx/paste/sendmail_mc.xD5s.txt (available until 2025-11-07 20:56:45 UTC) Cheers, K. C.