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Settings Emails Signing
Question asked by Miguel Enrique - 9/12/2023 at 11:56 AM
Answered
In delivery log and I find many errors of this type:

11:38:42.424 [27789236] Exception getting DKIM signature System.ArgumentException: The list of headers to sign SHOULD NOT include the 'Bcc' header.
Parameter name: headers
    at MimeKit.Cryptography.DkimSigner.Sign(FormatOptions options, MimeMessage message, IList`1 headers)
    at SmarterMail.Common.MailSigning.DKIM.DKIM.Sign(MimeMessage mime, db_domain_settings_readonly domainSettings, DkimSignatureField sigField, MessageSigningArgs signingArgs, List`1& logLines)
    at MailService.RelayServer.RemoteDeliverySession.GetDkimSignature()

I imagine that the sender has sent the email using some recipient in BBC. The email is sent to the recipient, but I do not know if it will be signed correctly with DKIM.

How should I configure the DKIM signing settings? 

Currently I have:

Key size: 2048 (Recommended)
Max messages: 0
Body canonicalization: Relaxed
Header canonicalization: Relaxed
Header fields to use: All non-repeatable fields

Should I change any?

Greetings.
Miguel Enrique.

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Miguel Enrique Replied
Hello.

Maybe I expressed myself wrong. English is not my native language and I use Google Translate a lot.

I would appreciate it if other SmarteMail users (administrators) who use DKIM signing could confirm if the configuration I am using is the same one they use.

Key size: 2048 (Recommended)
Max messages: 0
Body canonicalization: Relaxed
Header canonicalization: Relaxed
Header fields to use: All non-repeatable fields

Also, if someone uses SmarterMail 8629 (Aug 17, 2023), and has the same configuration that I use for DKIM signing, they could check if they have exceptions in their delivery logs with the following text: "Exception: The list of headers to sign SHOULD NOT include the 'Bcc' header"

I have sent emails that use BCC to dkimvalidator.com and it doesn't seem that SmarterMail includes the BCC header in the DKIM signature, so I don't really understand the exception.

Validation of dkimvalidator.com indicates that it is signed without BCC:

DKIM-Signature: v=1; a=rsa-sha256; d=monmariola.com; s=secure;
c=relaxed/relaxed; t=1694680295;
h=from:to:cc:subject:date:message-id:mime-version:x-mailer:thread-index:
x-declude-sender:x-declude-spoolname:x-declude-refid:x-declude-scan:
x-declude-tests:x-country-chain:x-declude-code:x-declude-recipcount:x-helo:
x-revdns:x-fpreview-weight;
bh=(omited);

Thank you
Miguel Enrique
Mon Mariola, S.L.
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Andrea Free Replied
Employee Post Marked As Answer
Hi Miguel,

Would you please open a support ticket? This will allow us to review the issue directly. There may be some debug logs thatyou can enable to help understand this behavior. 

Kind regards,
Andrea Free SmarterTools Inc. 877-357-6278 www.smartertools.com

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