DKIM is a cryptographic signature added to each outgoing email and checked by the receiver against a public key in your DNS. A match proves the message came from your domain and wasn't altered on the way. Each sending platform signs with its own key, published in DNS under its own name, called a selector.
Category
Deliverability
Also known as
DomainKeys Identified Mail; DKIM record; DKIM signature; DKIM selector
In practice
Publish DKIM for every sending platform separately. One missing selector means one tool's mail fails authentication while the rest passes. SPF and DKIM together are what DMARC evaluates.
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