DKIM
A cryptographic signature attached to outbound mail.
DomainKeys Identified Mail signs each message with a private key. Mailbox providers fetch the public key from DNS and verify the signature. DKIM proves the message was not tampered with and is critical for DMARC alignment.
reading this as SaaS product teams
A SaaS product sends on behalf of its customers, so the deciding factors are tenant isolation, whether suppressions can be scoped rather than global, and whether support can answer why one specific account did not receive one specific email. Lifecycle automation and transactional sending usually need to coexist.
Applied to dkim, that means weighing multi-tenant support, event stream, the suppressions API, and operating track record ahead of the rest, against trial expiry notices, dunning, onboarding sequences, and per-tenant transactional mail.