What It Is
DKIM stands for DomainKeys Identified Mail. When your email service sends a message, it attaches an invisible digital signature created with a private key. A matching public key is published in your domain’s DNS. The receiving server uses that public key to check the signature. It works like a wax seal on a letter: if the seal is intact and matches yours, the letter is genuine and has not been opened and changed.
Why It Matters for Your Business
DKIM is a key part of getting into the inbox. Google and Yahoo expect senders to use authentication such as SPF and DKIM, and bulk senders need both, plus DMARC. A yoga studio sending class reminders without DKIM may find many of them quietly filtered to spam, even though the messages themselves are perfectly ordinary.
Good to Know
Each service that sends email for you, such as your mailbox provider and your newsletter platform, usually needs its own DKIM key added to your DNS. Many providers walk you through it and then show a "verified" status once it works. Check that status after any change to your DNS or a website move, because DKIM records are easy to lose along the way.