When Office 365 users try to send email messages to one or more external domains, they receive one or more nondelivery reports (NDRs) that contain one of the following error codes:
550-DKIM: encountered the following problem validating
550 contoso.onmicrosoft.com: signature_incorrect
This issue may occur if the recipient domain doesn't comply with Domain Keys Identified Mail (DKIM) RFC 6376.
Do one of the following:
- Recommended method: Enable DKIM by creating a CNAME record for your domain in Office 365. For more information, see http://blogs.msdn.com/b/tzink/archive/2015/10/08/manually-hooking-up-dkim-signing-in-office-365.aspx.
- Contact the recipient domain and suggest that they comply with DKIM RFC 6376. Consider the message to be unsigned if a DKIM authentication failure occurs.
Article ID: 3145666 - Last Review: Dec 28, 2016 - Revision: 1
Microsoft Exchange Online, Microsoft Exchange Online Protection