Is there any reason specifically why I should set up DKIM keys for EACH of our clients on their own domains, vs. using the same DKIM key for ALL of our clients?
For example: say I setup DKIM keys on mydomain.com. I then instruct all of the clients who send campaigns themselves (not many, we setup and send for the majority of our clients) to - every time they setup a campaign - set the Sent From email address to firstname.lastname@example.org - and they can use their own email address for the Reply To address. This way, they're setup to use the authenticated DKIM keys, BUT they'll get replies anyways to their email@example.com address.
Partly I'm lazy, partly some of our clients host their sites in places where I can't get the DKIM set up, and partly I have no problem with using our domain that has DKIM keys already set up.
Am I missing something here? I'm not an email authentication expert - but this seems like a way that the system can be kind of "cheated" so that I set up authentication for ALL our clients at once - set it and forget it.
Anyone have any insight other than "it's the *right* way to do it"? What would be the disadvantages?
Edit: I see Campaign Monitor actually provides a FAQ on this process here - http://help.campaignmonitor.com/topic.aspx?t=108 - which makes me think it's a CORRECT way of setting up DKIM keys? Any evidence to the contrary?
You could do that for sure, but generally people want to send emails from their own domains rather than someone elses.
The Campaign Monitor help topic you reference is really intended for people who use the same domain in multiple related clients (like a company that sets up each store as a client under one account). They'd all naturally use the same corporate domain, and therefore the same domain keys.