DKIM for a domain not on my SmarterMail server ?
Question asked by ellisfr - 2/15/2022 at 7:49 AM
I have a SmarterMail server handling domainA.
One of my client as a domainB, we manage this domain and DNS, we host his website but his mail is on Office365.
His website send mail using our SmarterMail server.
We added our mail server in his domainB SPF record, that's ok.
But is there a way to declare our DKIM from SmarterMail (something like 12345._domainKey.domaina.com ) somewhere in domainB DNS ?

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Kyle Kerst Replied
Employee Post
You can absolutely publish a DKIM key for the domain and provide it to DomainB so that they can add this to DNS. You'd need to do that by adding the domain, then enabling DKIM as you would normally. 

That said, messages sent via their O365 environment will lack those DKIM signatures so you'll want to make sure their DMARC policy doesn't reject or quarantine those messages.
Kyle Kerst
System/Network Administrator
SmarterTools Inc.
(877) 357-6278
Douglas Foster Replied
DKIM signatures have a scope parameter, so that different entities can be given different scopes to use for different purposes.   Your client can probably configure DKIM signing on his O365 messages if desire, and he does not need to use the same private key as you are using.   Best practice will be to use a different scope (and key pair) for any O365 signatures.
ellisfr Replied
Thank you Kyle and Douglas for your help.

But if I add the domain on my SmarterMail, I'm afraid it will intercept mail sent to this domain and as mailboxes are not on this server, it will fail ?

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