DKIM, SPF, and DMARC are not just about making sure your marketing emails don't end up in spam. They protect against certain kinds of email spoofing, sending an email with a forged sender address. While it's a technique often used by spammers and is subsequently often filtered as such, it can also be used to perform phishing attacks against your organization and your customers.
I fear this article is a bit too technical for someone more on the marketing and less on the IT end of things.<p>Even organizations I would expect to get DKIM/SPF/DMARC right frequently don't. I don't know how many "Hey, I see your emails have DKIM/SPF problems, here is how to fix it," messages I've sent that nobody ever followed-through on.
Spam folders are just one thing. The big new death knell for email deliverability are the "clutter" folders. Most email clients now use a learning algorithm to opaquely filter newsletters and advertisements to their own folder.
I use MailChimp for newsletters and postmark for transactional email, and between the two have great deliverability. Both services, and many others, guide you through the process of setting all this up.
SPF, DKIM and DMARC are about authentication not deliverability. They do have some impact on deliverability but their primary usage is authentication. The main way that intersects with reputation is that properly authenticating allows various mailbox providers like gmail, et al to apply more weight to your domain reputation in their inbox placement algorithms.
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