DKIM fails when sending with Exchange Hybrid SMTP

Safak 20 Reputation points
2024-01-18T13:35:25.7266667+00:00

Hi, We have an exchange hybrid environment with a receive connector for SMTP. The settings for the receive connector looks like this: User's image

With following send connector: User's image

We are sending emails to external domains automatically via SMTP without authentication. If we enable DKIM it fails although we see the DKIM-Signature in the header.

Authentication-Results:

mx.google.com; dkim=fail header.i=@ourdomain.com header.s=selector2 header.b=aRRIv5Z9; dkim=fail header.i=@ourdomain.com header.s=selector2 header.b=aRRIv5Z9; arc=fail (signature failed); spf=pass (google.com: domain of @ourdomain.com designates as permitted sender) smtp.mailfrom=@ourdomain.com

X-MS-Exchange-Authentication-Results:

spf=pass (sender IP is xxx.xxx.xxx.xxx) smtp.mailfrom=ourdomain.com; dkim=fail (signature did not verify) header.d=ourdomain.com;dmarc=bestguesspass action=none header.from=Ourdomain.com;

Sending emails via Outlook or Outlook OWA doesn't have any DKIM problems.

How do I fix the DKIM failure when sending with Exchange Hybrid SMTP?

Microsoft Exchange Online
0 comments No comments
{count} votes

2 answers

Sort by: Most helpful
  1. Kael Yao-MSFT 37,696 Reputation points Microsoft Vendor
    2024-01-19T05:39:12.8+00:00

    Hi @Safak,

    Did you mean you enabled DKIM in Exchange Online?

    If yes, do the messages go to external recipients directly from Exchange Online? (on-premises to online to external, no other third-party gateways)

    If yes, does this issue only occur to certain recipients?

    Please also post the DKIM-Signature part of the message header.

    (Don't forget to hide your personal information) Example:

    DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=contoso.com; s=selector1-contoso-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=KEs42OsNdsrmiPfcVLwpIUZVT+vEuqqygMUN9vA+M2Y=; b=O8/rYT/jYym6TfYubf7UAvHIgqxqbd/RYnWn3KNV9Vc2yLrOOwEUtizwh1pwylLxJYIUKOdkrIEG7DOgqLG+xWLbURRsOTvt24yb1SlHBdTzzUcPHHVNaLFMWtGd3odEuGdjVXBmLdWsyR0s+8PUvqvqINoKrEqBAJm4VRts5ykZtD9RgcKndhQ0aWcWUTIbqagmFWmWkzDlvtW50T82C+KpLIW/SAPtzV/Vkss33HXqEOs05op/Xkca6IeJW1L5uNpv1jNceqnShZt8hIUWP5cjhYfwc9erFnjRjYQIndWVQ0wdoVpLN8GcCRp+Q92VgD09SZJwMuJlRI9kJo9kPw==
    

    If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".  Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.


  2. Amit Singh 5,071 Reputation points
    2024-01-22T05:59:53.5833333+00:00
    0 comments No comments

Your answer

Answers can be marked as Accepted Answers by the question author, which helps users to know the answer solved the author's problem.