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New Contributor II

How to enable FortiMail ARC Sealing



I would like to to enable ARC Sealing on a domain protected by FortiMail. I enabled ARC Sealing in the DKIM settings on the protected domain as advised by the the FortiMail Admin Guide. However, checking the mail header of a received mail, I do not see any ARC Sealing headers from FortiMail.


Our mail flow for incoming mails looks like this: Internet -> FortiMail -> Exchange Online.


I already tested different settings, such as ARC Sealing direction, DKIM signing on the Inbound Session profile, and disabled header removal. However, ARC Sealing was not done.


Any idea what I'm missing or what is exactly necessary to make FortiMail to "ARC seal" incoming mails before forwarding them to Microsoft?


Thank you.


Hello tokcum,

Thank you for using the Community Forum. I will seek to get you an answer or help. We will reply to this thread with an update as soon as possible.


Stephen - Fortinet Community Team

Hello tokcum,


We are still looking for someone to help you.

We will come back to you ASAP.


Stephen - Fortinet Community Team

Hello tokcum,


For now in FML ARC sealing option, in Incoming direction we only support header from or mail from which is a protected domain in FML

Incoming: Incoming email that has header from or mail from as a protected domain in FML (ARC sealing must be enabled in this domain advance setting).
For example, email from to and has been configured with ARC sealing in domain advance setting.

Outgoing: outgoing email that from an internal user to outbound user.

All: FML will do ARC sealing for emails that matched incoming/outgoing mentioned as above.




New Contributor

Hi Nagaraj


We have the same issue as tokcum - we never see any ARC-Seal from FML (V7.2.4), regardless of the sender and receiver domain and incoming or outgoing direction...


ARC-Sealing is configured as "All", DKIM is otherwise working as expected. What do we miss here?


Best Regards


New Contributor II

To enable ARC Sealing on FortiMail, make sure you have properly configured ARC Sealing in the DKIM settings for the protected domain. Check that the "Enable ARC Sealing" option is turned on. Ensure that ARC Sealing is configured in the correct direction for incoming emails and that DKIM signing is enabled in the Inbound Session profile. Additionally, verify that header removal is disabled, as this can interfere with ARC headers. If these settings are correct and you still don't see ARC headers, it might be a good idea to review the FortiMail logs for any errors or contact Fortinet support for further assistance.


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