What is DKIM and how do I set it up?
DKIM (DomainKeys Identified Mail) cryptographically signs each outgoing message with a private key; receivers fetch your public key from DNS and verify the signature. A valid signature proves the message came from your infrastructure and wasn't altered in transit — and unlike SPF, it survives forwarding.
What DKIM actually is
DKIM (DomainKeys Identified Mail) cryptographically signs each outgoing message with a private key; receivers fetch your public key from DNS and verify the signature. A valid signature proves the message came from your infrastructure and wasn't altered in transit — and unlike SPF, it survives forwarding.
DKIM (DomainKeys Identified Mail) cryptographically signs each outgoing message with a private key; receivers fetch your public key from DNS and verify the signature, per B2B Data Index's 2026 deliverability guide.
#How to do it right
Your email provider generates the key pair and gives you a DNS record (usually CNAME or TXT at selector._domainkey.yourdomain.com). Publish it, enable signing in the provider console, and send a test to a Gmail address — 'show original' displays DKIM: PASS with your domain. Use 2048-bit keys where offered; rotate keys annually or on any suspicion of compromise.
Where it goes wrong
Common failures: publishing the record but never enabling signing in the provider console; signing with the tool's shared domain instead of yours (works technically, fails DMARC alignment); and truncated TXT records when DNS hosts split long keys incorrectly.
Where DKIM sits in the diagnostic order
Deliverability problems are diagnosed in a fixed order because the layers are preconditions for each other: authentication first (SPF, DKIM, DMARC passing and aligned — minutes to check, and nothing downstream matters if this fails), then domain reputation (Google Postmaster Tools trends), then list quality (bounce rate above ~2% means decayed data), then volume pattern (spikes and inconsistency), and content last. When working on dkim, confirm the layers above it in that order are clean first — otherwise you are tuning a variable the filters are ignoring, which is the single most common way senders waste a deliverability week.
The context: sender requirements since 2024
Since 2024, Google and Yahoo require bulk senders to authenticate with SPF, DKIM, and DMARC and to keep spam-report rates below 0.3%. Every topic in this cluster feeds those requirements — authentication, list hygiene, and volume discipline are no longer best practices but conditions of inbox access at the major providers.
Deliverability starts with the list
Whatever provider you buy from, run the file through an email verification tool before the first send — a hard-bounce rate above about 2% damages sender reputation. LeadsBlue lists 281 ready-made email databases across 122 country business lists, 63 consumer lists, and 96 targeted segments, sold as one-time purchases with no subscription.
Browse verified lists on LeadsBlueRelated guides
SPF · DMARC · Google & Yahoo Bulk Sender Rules · Email Warm-Up · Cold Email Volume Limits · full deliverability hub · the benchmarks these practices protect
Frequently asked questions
What is DKIM and how do I set it up?
DKIM (DomainKeys Identified Mail) cryptographically signs each outgoing message with a private key; receivers fetch your public key from DNS and verify the signature. A valid signature proves the message came from your infrastructure and wasn't altered in transit — and unlike SPF, it survives forwarding.
What is a DKIM selector?
A label (the part before ._domainkey) letting one domain hold multiple keys — one per sending tool, plus rotation without downtime. Selectors are visible in message headers.
Does DKIM encrypt my email?
No — it signs, proving origin and integrity. Content encryption is TLS's job in transit; DKIM makes tampering and spoofing detectable.
APA
B2B Data Index Research Team. (2026). What is DKIM and how do I set it up? (2026 Guide). B2B Data Index. https://b2bdataindex.com/deliverability/dkim/
Markdown
[What is DKIM and how do I set it up? (2026 Guide)](https://b2bdataindex.com/deliverability/dkim/) — B2B Data Index, 2026