DKIM in Hybrid Environment

Question

We have a full hybrid installation and also utilize Barracuda for 3rd party gateway. Most mailboxes are located online but a few exist on on-prem server. We recently configured DMARC, DKIM and SPF and added the dmarc record and a DKIM CName record in our external DNS. All email incoming and outgoing go through on-prem server and out to Barracuda gateway (Barracuda is not pointed at online exchange). I am trying to verify this configuration specifically my DKIM configuration for this environment.

Answer 1

Yep, it does :)

You can use this for setting in 365:

https://learn.microsoft.com/en-us/microsoft-365/security/office-365-security/email-authentication-dkim-configure?view=o365-worldwide

Answer 2

No, if the messages are not going out through Exchange Online, then there is no way to stamp the DKIM info in the message header. The Barracuda server will need to handle this if thats how messages are sent outbound.

And yes, you would need to add the required DNS records in the external DNZ zone for each sending domain.

Answer 3

Send a message to another account ( personal gmail etc..) and then look at the headers to confirm its working

Or send a message here:

https://dkimvalidator.com/#:~:text=Just%20send%20an%20email%20to,as%20your%20actual%20SpamAssasin%20score.

You can also check your domain here:

https://mxtoolbox.com/dmarc/dmarc-email-tools?referrer=cms_dmarchome

https://easydmarc.com/tools/dkim-lookup

etc...