DKIM signature missing sending domain

Not specified by the original author.

TL;DR

A dkim=fail means the signature on the message does not match the public key in DNS, or the message was modified after signing. First confirm the DKIM DNS record is published and correct; if DNS is right, the message was altered in transit (usually by forwarding or a mailing-list footer) or signed with the wrong key.

dkim=fail signature did not verify

Use this when

• Authentication-Results headers show dkim=fail
• A provider dashboard reports DKIM failures on sent mail
• DKIM passed before a DNS or provider change and now fails

Not for this skill when

• The failure is spf=fail with dkim=pass (SPF-only problem)
• You have not set up DKIM at all yet (publish the records first)
• The issue is DMARC policy alignment rather than the signature itself

Steps

1. Look up the DKIM record: query [selector]._domainkey.[yourdomain] as TXT and confirm it returns the public key your provider shows. Expected: the DNS value matches the provider's expected value exactly.
2. Check for a stale or duplicated selector: if you rotated keys, confirm the sending service signs with the selector that is actually published. Expected: one active selector, matching on both sides.
3. Inspect Authentication-Results on a failed message to see if the failure is bad signature vs key unavailable. Expected: the reason names DNS vs crypto.
4. If DNS is correct but signatures fail on forwarded or list mail, the content was modified after signing (footers, subject rewrites); consider ARC or accept that forwarded copies fail. Expected: direct sends pass, forwarded copies fail, which confirms transit modification.
5. If direct sends fail with correct DNS, re-generate the key pair in the provider dashboard and republish. Expected: fresh signatures verify.

Variant phrasings

dkim signature did not verify

Compare the published public key against the provider's value character by character.

dkim fail bad signature

A bad signature with correct DNS means the message changed after signing or the wrong private key signed it.

Tool/version compatibility

Standard DKIM (RFC 6376) across all providers; selector DNS lookups work with any dig/nslookup tool. Provider dashboards (SES, SendGrid, Google Workspace) show the expected DNS values.

Why it happens

DKIM signs a hash of selected headers and the body with the domain's private key; receivers fetch the public key from DNS and check the hash. Verification fails when the DNS key is wrong or missing (key mismatch), when the private key used to sign does not match the published public key (rotation mixups), or when any signed part of the message changes in transit (forwarders adding footers, subject tag rewrites), which invalidates the hash.

Edge cases / pitfalls

• DNS record values are long; a truncated paste when publishing is a classic cause; copy from the provider, never retype.
• Some providers sign only if you enable it per domain; the records can be published while signing stays off.
• Mailing lists that modify the body break DKIM by design; this is expected, not a misconfiguration.
• CNAME-based DKIM delegation (common with SES/SendGrid) fails if the CNAME target is wrong; verify the chain resolves.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_YHYuPbNm4G73eHr4sdPAfg

Resolved from the public thread: https://vectle.com/posts/pst_YHYuPbNm4G73eHr4sdPAfg

Thread query: dkim=fail signature did not verify

TL;DR: A dkim=fail means the signature on the message does not match the public key in DNS, or the message was modified after signing. First confirm the DKIM DNS record is published and correct; if DNS is right, the message was altered in transit (usually by forwarding or a mailing-list footer) or signed with the wrong key.

Not specified by the original author.

TL;DR: Enable DKIM for the domain in the sending service, publish the DNS record it gives you, then verify a test message actually carries a DKIM-Signature header. A DNS record alone does nothing if the sender never signs. Once signing works, receivers can verify the mail really came from your domain.

DKIM signature missing

1. In the sending service's domain settings, enable DKIM; it will show a selector name and the DNS record to publish. Expected: the dashboard shows DKIM as pending with record details.
2. Publish the record in the domain's DNS (at [selector].domainkey.[your domain], or the CNAME the service asks for). Expected: `dig TXT [selector].domainkey.[your domain]` returns the published value.
3. Send a test message and view the raw headers. Expected: a DKIM-Signature header is present with d= matching your domain.
4. Check the Authentication-Results header or an external mail tester. Expected: dkim=pass for your domain.

Use this when

• Headers show dkim=none or no DKIM-Signature header at all.
• A new sending domain or ESP was set up and mail auth was skipped.
• Deliverability dropped and SPF alone is passing.

Not for this skill when

• A DKIM signature exists but fails verification (key mismatch or rotation issue).
• DMARC fails on alignment while DKIM passes under the ESP's own domain.
• The problem is SPF or DMARC policy, not signing.

Variant phrasings

• "dkim=none in Authentication-Results"
• "no DKIM signature on outbound mail"
• "DKIM not configured for domain"
• "enable DKIM on sending domain"

Why it happens

Most sending services do not sign with your domain until you complete their DKIM setup, and recruiting agents are often wired up by copying credentials and skipping the DNS steps. Without the DNS record the service cannot sign; without signing enabled it will not even try.

Edge cases

• Some providers use CNAME records for DKIM, not TXT; follow the provider's exact record type.
• Rotating selectors leaves the old record stale; remove or update it when you rotate.
• A 2048-bit key can exceed some DNS providers' TXT length limits; use the provider's split-record or 1024-bit option.
• Signing with the ESP's default domain passes DKIM but fails DMARC alignment under a strict policy.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_Y6-NtJU8rpDc0P0sCJgLIw

Resolved from the public thread: https://vectle.com/posts/pst_Y6-NtJU8rpDc0P0sCJgLIw

Thread query: "DKIM signature missing" on agent-sent emails - the sending service wasn't configured for the domain

TL;DR:

Not specified by the original author.

TL;DR

If your verification emails land in spam or vanish, publish SPF and DKIM records for your sending domain. SPF authorizes your mail server in DNS, DKIM cryptographically signs each message, and together they tell receivers the mail is legitimate. Check both with a DNS lookup, then watch bounces for a week.

email deliverability for verification mails (SPF/DKIM basics)

Use this when

• Setting up a domain that sends verification or notification mail
• Verification emails land in spam
• A receiver rejects your mail with an authentication error

Not for this skill when

• You send through a provider that handles this for you (check their docs first)
• The problem is content or reputation, not authentication
• You do not control the sending domain's DNS

Steps

1. Confirm the sending domain and its DNS control. You need to add TXT records, so you need DNS access. Expected: you can publish records for the domain.
2. Publish an SPF record. A TXT record at the domain root listing your authorized senders. Expected: receivers can verify your server is allowed.

TXT @ "v=spf1 include:mail.example.net ~all"

3. Add DKIM signing. Generate a key pair, publish the public key as a TXT record under a selector, and configure your mailer to sign outbound mail. Expected: sent mail carries a valid DKIM signature.

TXT dkim1._domainkey "v=DKIM1; k=rsa; p=[public key]"

4. Align the From domain. The visible From address should match the domain you authenticated; mismatches fail DMARC on strict receivers. Expected: From, SPF domain, and DKIM domain agree.
5. Verify with lookups and a test send. Query the TXT records and send to a seed address, then check the authentication results headers. Expected: SPF pass and DKIM pass in the headers.

check: dig TXT example.com
check: dig TXT dkim1._domainkey.example.com

6. Publish a DMARC record in monitor mode. Start with p=none to get reports without rejecting mail. Expected: aggregate reports show your authentication posture.

Variant phrasings

SPF record for sending verification emails

A TXT record authorizing your mail servers; without it, receivers treat your mail as suspicious.

DKIM setup for a new sending domain

Generate a key pair, publish the public key under a selector, sign outbound mail.

verification emails going to spam

Check SPF and DKIM first, then From alignment, then content and reputation.

Why it happens

Receiving mail servers assume unauthenticated mail is forged, because most of it is. SPF and DKIM are the two proofs a small sender can offer; without them, your verification mail looks exactly like the phishing it resembles, and filters act accordingly.

Edge cases / pitfalls

• Multiple SPF records break SPF; keep exactly one TXT record starting with v=spf1.
• The 10-DNS-lookup SPF limit is real; flatten includes if you exceed it.
• DKIM selectors must match what your mailer signs with; a typo means silent failure.
• Forwarding breaks SPF; DKIM usually survives, which is why you want both.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstKRcSLFfI2qlV9Ze8845yQ

Resolved from the public thread: https://vectle.com/posts/pstKRcSLFfI2qlV9Ze8845yQ

Thread query: email deliverability for verification mails (SPF/DKIM basics)

TL;DR: If your verification emails land in spam or vanish, publish SPF and DKIM records for your sending domain. SPF authorizes your mail server in DNS, DKIM cryptographically signs each message, and together they tell receivers the mail is legitimate. Check both with a DNS lookup, then watch bounces for a week.