Scenario
You are using Exclaimer Server-Side email signatures and notices that DKIM headers are missing or removed from messages after processing. This can lead to questions about whether Exclaimer supports DKIM, re-signs emails, or applies Authenticated Received Chain (ARC) sealing.
Reason
DomainKeys Identified Mail (DKIM) works by applying a digital signature based on the exact content of an email message.
When Exclaimer applies a Server-Side signature, the message content is modified and because of this change:
Any existing DKIM signature becomes invalid
The DKIM signature is therefore removed during processing
Exclaimer does not DKIM sign or re-sign emails, does not apply ARC sealing, and cannot be configured to DKIM sign mail on return connectors.
Resolution
This behavior is expected and does not require any additional configuration.
After Exclaimer finishes processing the message, it is returned to Microsoft 365 or Google Workspace, which automatically applies a new DKIM signature for external delivery.
• DKIM is removed only when a Server-Side signature is applied.
• Internal messages may not always display DKIM headers.
• External messages are automatically DKIM signed by Microsoft 365 or Google Workspace.
• Exclaimer does not provide DKIM signing or ARC sealing itself.
Exclaimer does not sign outbound mail using customer DKIM keys and does not apply ARC seals. DKIM signing is performed by the final sending platform (Microsoft 365 or Google Workspace) after Exclaimer has finished modifying the message.
ARC sealing is not currently supported, but may be considered as a future enhancement.