DKIM
Also called: DomainKeys Identified Mail
DKIM (DomainKeys Identified Mail) adds a cryptographic signature to each email, with the public key published in your DNS, proving the message wasn’t altered and that your domain took responsibility for it.
Your mailbox provider signs outgoing mail with a private key and gives you a DNS record (under a “selector” such as google._domainkey) holding the public key. Receivers fetch it and check the signature.
Gmail requires DKIM keys of at least 1024 bits for mail to personal Gmail accounts and recommends 2048 bits where your provider supports it (Google).
How it affects cold email
DKIM is required by Gmail and Yahoo for bulk senders, and by Outlook.com for domains sending more than 5,000 emails a day (Microsoft).
One-click unsubscribe also depends on it: RFC 8058 says both unsubscribe headers must be covered by a valid DKIM signature (RFC 8058).
How Inboxed handles it
- Turn DKIM on in your mailbox provider’s admin console and publish the record it gives you. Inboxed’s domain checker looks for DKIM records at common selectors and tells you if it can’t find one.
Related terms
Sources
Sources checked on 8 November 2026. Rules change, so check the source before you rely on a detail.
- Email sender guidelines · Google, Gmail Help
- Strengthening Email Ecosystem: Outlook’s New Requirements for High‐Volume Senders · Microsoft Tech Community
- RFC 8058: Signaling One-Click Functionality for List Email Headers · IETF / RFC Editor
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