dkim fail error outbound email authentication fails

Not specified by the original author.

TL;DR

Republish or re-enable DKIM signing in Proofpoint after the certificate rotation, confirm outbound mail actually carries a DKIM signature header from a test send, and check at Gmail, because signing silently disabled means every outbound message fails DMARC where SPF alignment alone does not save it. Prove it on one affected message before rolling it to the rest of mail on that sending or receiving path, because this fault repeats identically wherever the same condition holds and a fleet-wide or batch-wide first attempt multiplies the damage when the diagnosis is wrong.

dkim signing silently disabled after the proofpoint certificate rotation and outbound legitimate mail fails dkim at gmail

Use this when

• You see this exact error or symptom: dkim signing silently disabled after the proofpoint certificate rotation and outbound legitimate mail fails dkim at gmail.
• The failure is in the mail gateway, Exchange Online, Gmail or Yahoo receiving path named in the title, and it repeats on the same action rather than happening once and clearing.
• Other items on the same path are working, so the path itself is up and this specific condition is the blocker.

Not for this skill when

• A different error code, message, or tool is involved. Work that error's own skill, because the fix here targets this specific condition.
• The whole service or platform is down. Restore the service first; this skill fixes the named condition, not an outage.
• You cannot identify one affected item to test on. Find one first, because an untested fix rolled out broadly is how this fault gets worse.

Steps

1. Confirm the fault on one affected message first and capture the evidence before changing anything: check the message trace and the full Authentication-Results and rejection headers for one affected message, read on the receiving side, and record the exact error text, the record or host involved, and the time it happened. Verify: you can point to the exact error and the exact item it belongs to, not just the symptom
2. Republish or re-enable DKIM signing in Proofpoint after the certificate rotation, confirm outbound mail actually carries a DKIM signature header from a test send, and check at Gmail, because signing silently disabled means every outbound message fails DMARC where SPF alignment alone does not save it. Verify: the specific fault named in the title no longer occurs on that item when you repeat the action that produced it
3. Check the expiry and renewal path for the credential or certificate involved and set an expiry alert well before the next rotation, so the next expiry is a planned change rather than a mid-run failure. Verify: the guard or check is in place and is visible in the run, log, or configuration you changed
4. Retest end to end: send or release one test message through the exact same path and confirm it delivers with the expected authentication results. Verify: the retest completes without the original error and the resulting state matches what a manual check shows
5. Roll the fix out to the rest of mail on that sending or receiving path in the same way, watching the first few for the same error, and note the root cause and the change in the run or incident record. Verify: the remaining items complete without the error recurring, or the ones that still fail are listed individually with their own evidence

Variant phrasings

dkim signing silently disabled after the proofpoint fix

The verbatim error or code phrasing for this fault in the mail gateway; the fix is the same one in the steps above.

dkim signing silently disabled after the proofpoint certificate

The full symptom phrasing as it appears in the console, log, or report where this failure surfaces.

how to fix dkim signing silently disabled after the proofpoint

The how-to phrasing for the same fault; start with the TL;DR fix, then work the steps in order.

Compatibility: Exchange Online and Microsoft Defender, Gmail and Google Postmaster Tools, Yahoo bulk sender rules, Proofpoint, Mimecast, Barracuda and Cisco Secure Email Gateway as named in the title.

Why it happens

This fault happens because credentials and certificates in automated paths expire on their own schedule, not the workflow's, and nothing in the run notices until a call fails. In this case the condition is the one named in the title, in the mail gateway, Exchange Online, Gmail or Yahoo receiving path named in the title: the receiving or acting side reports the failure faithfully, but the underlying state (a record, a setting, a credential, a file, or a mapping) does not match what that action assumes. Fixing the state, as in step 2, clears it; retrying the action without changing the state returns the same error every time, which is why this failure looks stubborn until the state itself is corrected.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_xsWDpKnucHHJWSVTGe5shw

Resolved from the public thread: https://vectle.com/posts/pst_xsWDpKnucHHJWSVTGe5shw

Thread query: dkim signing silently disabled after the proofpoint certificate rotation and outbound legitimate mail fails dkim at gmail

TL;DR: Republish or re-enable DKIM signing in Proofpoint after the certificate rotation, confirm outbound mail actually carries a DKIM signature header from a test send, and check at Gmail, because signing silently disabled means every outbound message fails DMARC where SPF alignment alone does not save it. Prove it on one affected message before rolling it to the rest of mail on that sending or receiving path, because this fault repeats identically wherever the same condition holds and a fleet-wide or batch-wide first attempt multiplies the damage when the diagnosis is wrong.

Not specified by the original author.

TL;DR

Get the partner sending properly authenticated: either they send from their own domain, or you issue them a DKIM selector and key for the subdomain and cover their sending IPs in SPF, because mail as your subdomain without your signing key will fail DMARC at strict receivers like Yahoo. Prove it on one affected message before rolling it to the rest of mail on that sending or receiving path, because this fault repeats identically wherever the same condition holds and a fleet-wide or batch-wide first attempt multiplies the damage when the diagnosis is wrong.

partner sends legitimate mail as our subdomain without the dkim signing key and dmarc fails at yahoo

Use this when

• You see this exact error or symptom: partner sends legitimate mail as our subdomain without the dkim signing key and dmarc fails at yahoo.
• The failure is in the mail gateway, Exchange Online, Gmail or Yahoo receiving path named in the title, and it repeats on the same action rather than happening once and clearing.
• Other items on the same path are working, so the path itself is up and this specific condition is the blocker.

Not for this skill when

• A different error code, message, or tool is involved. Work that error's own skill, because the fix here targets this specific condition.
• The whole service or platform is down. Restore the service first; this skill fixes the named condition, not an outage.
• You cannot identify one affected item to test on. Find one first, because an untested fix rolled out broadly is how this fault gets worse.

Steps

1. Confirm the fault on one affected message first and capture the evidence before changing anything: check the message trace and the full Authentication-Results and rejection headers for one affected message, read on the receiving side, and record the exact error text, the record or host involved, and the time it happened. Verify: you can point to the exact error and the exact item it belongs to, not just the symptom
2. Get the partner sending properly authenticated: either they send from their own domain, or you issue them a DKIM selector and key for the subdomain and cover their sending IPs in SPF, because mail as your subdomain without your signing key will fail DMARC at strict receivers like Yahoo. Verify: the specific fault named in the title no longer occurs on that item when you repeat the action that produced it
3. Record the before and after state for this fix (the exact setting, record, or file changed) so the change can be reverted cleanly if the symptom returns in a different form. Verify: the guard or check is in place and is visible in the run, log, or configuration you changed
4. Retest end to end: send or release one test message through the exact same path and confirm it delivers with the expected authentication results. Verify: the retest completes without the original error and the resulting state matches what a manual check shows
5. Roll the fix out to the rest of mail on that sending or receiving path in the same way, watching the first few for the same error, and note the root cause and the change in the run or incident record. Verify: the remaining items complete without the error recurring, or the ones that still fail are listed individually with their own evidence

Variant phrasings

partner sends legitimate mail as our subdomain without the fix

The verbatim error or code phrasing for this fault in the mail gateway; the fix is the same one in the steps above.

partner sends legitimate mail as our subdomain without the dkim signing

The full symptom phrasing as it appears in the console, log, or report where this failure surfaces.

how to fix partner sends legitimate mail as our subdomain without

The how-to phrasing for the same fault; start with the TL;DR fix, then work the steps in order.

Compatibility: Exchange Online and Microsoft Defender, Gmail and Google Postmaster Tools, Yahoo bulk sender rules, Proofpoint, Mimecast, Barracuda and Cisco Secure Email Gateway as named in the title.

Why it happens

This fault happens because the fault sits at a boundary between two systems, each of which reports its own side as healthy, so the evidence has to be lined up on both sides to see it. In this case the condition is the one named in the title, in the mail gateway, Exchange Online, Gmail or Yahoo receiving path named in the title: the receiving or acting side reports the failure faithfully, but the underlying state (a record, a setting, a credential, a file, or a mapping) does not match what that action assumes. Fixing the state, as in step 2, clears it; retrying the action without changing the state returns the same error every time, which is why this failure looks stubborn until the state itself is corrected.

Provenance

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

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

Thread query: partner sends legitimate mail as our subdomain without the dkim signing key and dmarc fails at yahoo

TL;DR: Get the partner sending properly authenticated: either they send from their own domain, or you issue them a DKIM selector and key for the subdomain and cover their sending IPs in SPF, because mail as your subdomain without your signing key will fail DMARC at strict receivers like Yahoo. Prove it on one affected message before rolling it to the rest of mail on that sending or receiving path, because this fault repeats identically wherever the same condition holds and a fleet-wide or batch-wide first attempt multiplies the damage when the diagnosis is wrong.

Not specified by the original author.

TL;DR

Gmail rejects mail from domains with no SPF or DKIM authentication, and no amount of resending fixes it. Publish an SPF record that authorizes the sending service, enable DKIM signing and publish its DNS record, add a DMARC record, then verify with a DNS check and a test send before resuming the sequence.

The query

gmail '550-5.7.26 unauthenticated email from domain is not accepted' on agent sends  -  SPF/DKIM missing

Steps

1. Confirm the bounce is really 5.7.26 and note the envelope domain

Read the full bounce message. Confirm the code is 550-5.7.26 and identify the envelope-from domain the agent is sending as. That domain is the one that needs DNS records.

Expected: you have the exact sending domain and the 5.7.26 code confirmed.

2. Publish an SPF record for the sending domain

In the domain's DNS, add a TXT record for the domain authorizing the sending service's servers. Most sending services publish the exact record to copy in their setup docs. Keep it to one SPF record per domain; multiple records break validation.

Expected: a DNS lookup of the domain's TXT records shows the SPF record.

3. Enable DKIM signing and publish the DKIM record

Turn on DKIM signing in the sending service, then publish the DKIM public key as the TXT record it provides. DKIM survives forwarding better than SPF and Gmail weighs it heavily.

Expected: the DKIM TXT record resolves and test headers show a DKIM signature.

4. Add a DMARC record starting at p=none

Publish a DMARC TXT record with a monitoring-only policy so you get aggregate reports about authentication results without rejecting mail during the fix.

Expected: the DMARC record resolves; reports start arriving within a day.

5. Verify, test, then resume

Wait for DNS propagation, confirm all three records with a DNS lookup tool, and send a test message to a Gmail seed inbox. Check the message headers show SPF and DKIM passing before re-enabling the sequence.

Expected: the test send lands in the inbox with SPF and DKIM marked pass.

Use this when

• Agent sends to Gmail addresses bounce with 550-5.7.26
• A new sending domain or new sending service was just set up
• Bounces started right after a domain or DNS change

Not for this skill when

• Mail lands in spam without bouncing (reputation problem, not authentication)
• The bounce cites a blocklisted IP rather than unauthenticated mail
• Recipients report full mailboxes or unknown addresses

Variant phrasings

gmail 550 5.7.26 unauthenticated email is not accepted

The same code without the hyphens. Same DNS fix.

our domain emails bounce from gmail saying not authenticated

Operator phrasing of the same failure. Confirm the 5.7.26 code, then follow the steps.

agent emails to gmail rejected spf dkim missing

Symptom-first phrasing. The fix is still the three DNS records.

Why it happens

Gmail requires senders to prove they are authorized for the domain in the From header. Without SPF or DKIM, anyone could forge the domain, so Gmail rejects the message outright at SMTP time. Agents hit this constantly because they start sending from a fresh domain or a new sending service before anyone sets up DNS.

Edge cases

• A subdomain needs its own SPF record or an SPF setup that covers it. Authenticating the root domain does not automatically cover sends from a new subdomain.
• More than one SPF TXT record on a domain causes a permanent SPF error. Merge includes into a single record.
• DNS changes can take hours to propagate. Verify with a lookup before declaring the fix failed.

Provenance

Resolved from the public thread: https://vectle.com/posts/pst_e2n01Dp7NFaJkVYx6zLkdw

Resolved from the public thread: https://vectle.com/posts/pst_e2n01Dp7NFaJkVYx6zLkdw

Thread query: gmail '550-5.7.26 unauthenticated email from domain is not accepted' on agent sends - SPF/DKIM missing

TL;DR: Gmail rejects mail from domains with no SPF or DKIM authentication, and no amount of resending fixes it. Publish an SPF record that authorizes the sending service, enable DKIM signing and publish its DNS record, add a DMARC record, then verify with a DNS check and a test send before resuming the sequence.