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The requirements and troubleshooting details below are specific to Google’s guidance for Gmail and Google Workspace unless stated otherwise. Other mailbox providers can apply different rules.
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1. Inspect a real message before changing DNS
Send a controlled test from the same system that produced the spam-foldered mail to an account at the affected provider. In Gmail, open the message and choose More → Show original. Google’s Messageheader tool can also help analyze headers. Capture the full headers and note:
- The recipient provider and approximate send time.
- The visible
From:address and theReturn-Path:(the envelope sender used for SPF evaluation). - The
Authentication-Results:values for SPF, DKIM and DMARC. - The sending IP, and whether the message was delivered to the inbox, delivered to spam, rejected or deferred.
Test each sending path separately. A message from your mailbox provider may authenticate correctly while a website form, CRM, support desk or billing platform does not. Google says authentication results appear in message headers and recommends using headers to troubleshoot a specific message.
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2. Read the authentication results correctly
| Header result | What it establishes | What to check next |
|---|---|---|
spf=pass |
The connecting sender was authorized under the SPF policy for the evaluated envelope identity. | Compare that identity with the visible From domain. SPF passing alone does not prove alignment. |
dkim=pass |
The message’s DKIM signature verified for its signing domain. | Compare the signature’s d= domain with the visible From domain under the receiver’s alignment rules. |
dmarc=pass |
At least one passing SPF or DKIM identity aligned with the visible From domain under the applicable DMARC policy. | If DMARC fails, find out whether SPF or DKIM failed, or passed without alignment. |
The visible From domain and SPF’s envelope identity are different fields. That distinction often explains why a message can show spf=pass but still fail DMARC. For direct mail to personal Gmail, Google says the visible From domain must align with either SPF or DKIM for its stated bulk-sender requirement; Google recommends aligning both where practical.
3. Audit SPF across all the services that send your mail
Inventory every sending system
List every service that sends using your domain, including your mailbox host, website forms, CRM, newsletter platform, invoicing or billing system, support desk and applications. Confirm that each service is authorized by the SPF policy for the domain it uses. If a legitimate service is missing, its mail may fail SPF even if mail from your main mailbox provider passes.
Check the record and its DNS lookup count
There should be one SPF record for a given domain, and it should cover all active senders. Google Workspace Help says the SPF specification permits a maximum of 10 DNS lookups; nested lookups count toward that limit. Multiple SPF records, typos, incorrect qualifiers, omitted senders or too many lookups can cause SPF failures. Remove obsolete services instead of adding every possible include.
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4. Verify DKIM for the specific sending provider
DKIM is configured per sending service: a working key for one platform does not prove that another platform is signing mail correctly. In the affected message, inspect the DKIM-Signature values for s= (selector) and d= (signing domain). Confirm that the selector’s DNS TXT record is published at the name expected by the provider and contains the correct key.
Google identifies an incorrect published key and changes to signed message content during transit as possible reasons for DKIM verification failure. If a forwarding service or intermediary modifies the signed message, ask whether it can avoid altering the signed content. For personal Gmail, Google requires a DKIM key of at least 1024 bits and recommends 2048 bits where the provider supports it. These are Gmail authentication requirements, not a promise of inbox placement.
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5. Check DMARC alignment before tightening policy
DMARC passes when SPF or DKIM passes with an identity aligned to the visible From domain. Compare the domains in the message headers with the DMARC record’s alignment settings. Under strict alignment, the domains must match exactly; relaxed alignment permits matching organizational domains. A provider that sends from a different subdomain can therefore pass authentication but fail strict alignment.
Review DMARC aggregate reports to see which sending source is failing and why. Google’s troubleshooting guidance says to enable SPF and DKIM for at least 48 hours before enabling DMARC. Do not move to a stricter enforcement policy such as p=quarantine or p=reject until legitimate mail streams are authenticated and aligned; otherwise, valid mail may be sent to spam or rejected.
A DMARC policy of p=none is not, by itself, proof that DMARC caused spam placement. Google says mail can go to spam for reasons other than the DMARC record, and its bulk-sender guidance permits a DMARC policy of none.
6. If authentication passes, investigate delivery and sender practices
When SPF, DKIM and DMARC all pass, move beyond DNS. Google says unwanted mail and recipient spam reports can affect whether future messages are marked as spam. Check whether recipients expected the message, whether they opted in, whether complaint levels have changed, whether sending volume rose suddenly, and whether sender identity and message categories are consistent.
For senders sending more than 5,000 messages per day to Gmail accounts, Google’s requirements, which began February 1, 2024, include SPF, DKIM and DMARC; valid forward and reverse DNS (including PTR); TLS; and RFC 5322-compliant formatting. Google’s guidance says the spam rate reported in Postmaster Tools should stay below 0.30%. Relevant marketing and subscribed messages must support one-click unsubscribe and include a visible unsubscribe link in the message body. These are Gmail requirements and guidance, not universal rules for every mailbox provider.
For that Gmail bulk-sender alignment requirement, the visible From domain must align with SPF or DKIM. Google recommends alignment with both for reliability. Its mitigation path applies only to bulk senders meeting all applicable requirements, including spam-rate and unsubscribe rules.
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7. Monitor the fix and verify it with another message
Use Google Postmaster Tools to review Gmail compliance status, authentication, delivery errors, spam reports and message-format indicators. A dashboard showing no authentication for a domain that does not send mail is not evidence of a failure; interpret it alongside actual sending activity. Google recommends checking DMARC reports for more detail and points to third-party tools for analyzing them.
- Save one original header from a failed test and note which sending system produced it.
- Make the narrowest relevant correction: authorize an omitted SPF sender, repair the provider’s DKIM key, or fix the specific alignment mismatch.
- Record when the DNS change was made and allow the applicable propagation time before judging it.
- Send another test through the same system, inspect its headers and confirm the new authentication results.
- Continue monitoring placement and Gmail indicators; a successful authentication retest does not establish that reputation or other delivery issues are resolved.
Choose the fix that matches the failure
| Evidence | Likely layer to investigate | Safer next action |
|---|---|---|
spf=fail for one sending service |
SPF authorization, record syntax or DNS lookup limit | Check that service’s documented SPF instructions and consolidate authorization into one valid record. |
dkim=fail or no valid signature |
Provider selector, published key or message modification | Compare the message’s selector and signing domain with the provider’s DNS setup. |
SPF or DKIM passes, but dmarc=fail |
Alignment between the authenticated identity and visible From domain | Use headers and aggregate reports to identify the mismatched identity; review strict versus relaxed alignment. |
| All three pass, but mail lands in spam | Recipient complaints, sending practices or other provider requirements | Review consent, volume, Postmaster Tools signals and the applicable provider’s technical requirements. |
Make a targeted change based on the message evidence rather than tightening DMARC or adding broad SPF entries by default. The same symptom—mail in spam—can originate in authentication, alignment, reputation or provider-specific requirements.
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