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Inventory every stream before you touch the policy
Start with a list of the domains that appear in the visible From header, their organizational domains, and any subdomains that send mail. Then list every system that sends on their behalf. That usually includes:
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- Internal application mail, such as password resets, alerts from monitoring tools, and scheduled reports from line-of-business systems
- Transactional mail from an ecommerce platform, billing system, or help desk
- Marketing and newsletter platforms, including any separate sending subdomain they use
- Collaboration and office suites that send notifications or invitations
- Occasional or seasonal senders, such as a survey tool used once a quarter or a holiday campaign vendor
Expect surprises. A report from an unfamiliar sending address is often an authorized service whose configuration is incomplete, not a spoofing attempt. Treat it as an open question until the owning team or vendor confirms it.
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Make SPF and DKIM align with the From domain
DMARC does not ask whether SPF or DKIM passed in isolation. It asks whether an authenticated identifier that passed also matches the visible From domain under the alignment rules. SPF is checked against the envelope sender (the bounce or Return-Path domain). DKIM is checked against the signing domain in the d= tag of the signature. If either one passes and aligns, DMARC passes for that message. The sequence below relies on this: one aligned path is sufficient for DMARC, but you should not treat one path as enough for your whole mail stream.
RFC 9989, the current DMARC specification at the RFC Editor, directs domain owners to configure aligned SPF and DKIM identifiers and prefers two aligned authenticated identifiers. The second path matters when one mechanism breaks. A forwarded message can fail SPF because the forwarder is not in your SPF record, and a message altered in transit can fail DKIM because the body changed after signing. Having both paths aligned keeps the stream passing in those cases.
In practice, check each stream for these points:
- The SPF record includes the sending platform, and the envelope sender uses a domain you control or one that aligns with your From domain.
- DKIM is signed with a
d=domain that matches your From domain under your chosen alignment mode, typically by configuring a custom DKIM domain in the vendor’s control panel. - A vendor that signs with its own domain (for example,
d=vendor.example) and uses a bounce domain you do not control produces no aligned path for your From address. That stream needs a vendor setting change or a different configuration.
Publish a monitoring policy with a reporting address
Record syntax
Publish a TXT record at the _dmarc label of your domain. Microsoft’s guidance for Microsoft 365 documents the hostname and basic structure in its DMARC setup article. A monitoring-only record looks like this:
_dmarc.example.com TXT "v=DMARC1; p=none; rua=mailto:[email protected]"Google’s sender guidelines require the v and p tags to come first in the record. Keep that order even when you add more tags. After publishing, confirm the record with a DNS lookup from outside your network, and confirm that the TXT value is a single record; two DMARC records at the same label cause the policy to be ignored.
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The rua tag sends aggregate XML reports to a mailbox. Google warns that report volume can be high, so decide before you publish who will receive these messages. Three options are common:
- A dedicated mailbox or group that is monitored by a named person or team
- An internal parser that extracts the XML and loads results into a dashboard or spreadsheet
- A third-party report-processing service that parses reports on your behalf
If the reporting mailbox sits on a different organizational domain than the one publishing the policy, that receiving domain must publish a DNS authorization record before receivers will deliver reports to it. Check the destination’s current DMARC documentation for the exact record format, because it is easy to overlook and reports silently stop arriving.
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Google does not support ruf, the failure-report tag. Do not make failure reports a required part of your plan. Aggregate data is the working input for the rest of the rollout.
Confirm the rollout is working by checking that reports arrive from at least one major receiver within a few days of publishing. If nothing arrives, check the DNS record and the destination’s authorization first.
Read aggregate reports for what they can establish
Each aggregate report groups message results by sending source, with counts and the outcome of SPF, DKIM, and alignment checks. Group the data by sending source, volume, SPF result and alignment, DKIM result and alignment, and receiver disposition. That view tells you which streams already pass, which fail, and why.
Aggregate reports are useful, but they have limits that shape how you act on them:
- They are not a complete inventory. A sender that rarely sends, or that sends through a path the reporting receivers do not see, may not appear in the reporting period you reviewed.
- They do not show what a user saw. Reports record authentication results and receiver disposition, not whether a message reached an inbox or a spam folder for a particular recipient.
- They do not explain intent. A failing source may be a misconfigured vendor or an attacker; the report alone does not say which.
- Coverage depends on which receivers send reports. Results from one provider are a view of that provider’s traffic, not of all mail.
Use the reports to build a list of sources and their status, then investigate each one. The DMARC.org overview describes this staged deployment in the same general order.
Remediate legitimate mail before raising enforcement
Each legitimate stream that fails must be fixed at the sender, not by weakening your policy. The most common causes fall into four groups.
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SPF is missing the sending platform
The stream’s envelope sender is not authorized by your SPF record. Ask the vendor for the include mechanism or IP ranges they require, add them to the record, and keep the record under the DNS lookup limit that SPF enforces. Re-check reports after the change, because one fixed source can reveal another behind it.
DKIM is not signing, or signs with the wrong domain
Ask the vendor to enable custom DKIM signing for your domain and to publish the selector records they provide. Confirm a test message carries a DKIM-Signature header whose d= value matches your From domain.
Alignment fails even though authentication passes
A message can pass SPF for its own envelope domain yet fail DMARC because that domain does not align with the From address. The fix is usually the vendor’s custom bounce domain or DKIM domain setting, not a DNS change in your zone.
Forwarding and list traffic break the path
Forwarded mail and mailing-list messages can change the envelope sender or the body. Those messages often rely on the DKIM path. If a stream of this kind fails, verify that the originating system signs with an aligned domain and that the intermediary does not alter the signed content.
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After each change, keep monitoring. Do not assume a fix is complete until the next reporting cycle shows the stream passing.
Raise enforcement in stages
Move to quarantine
Move to p=quarantine only after the legitimate streams you found are accounted for and aligned. Microsoft’s guidance suggests starting with a lower-volume domain or subdomain. Its documented example raises the pct value in steps of 10, 25, 50, 75, and then 100. Those values are an example from one provider, not a required schedule.
v=DMARC1; p=quarantine; pct=10; rua=mailto:[email protected]During each step, watch for two signals: legitimate mail landing in spam, and new senders appearing in reports that were not in your inventory. Either one means you pause the increase and fix the cause.
Move to reject
After the quarantine phase is stable and known legitimate streams continue to pass, progress to p=reject. Keep the same watch on reports and on user-facing delivery problems such as complaints about missing invoices or password reset messages.
Keep a rollback plan ready. If legitimate mail is affected, return to the previous policy, identify the missed sender or alignment issue, correct it, and then resume the increase. A pct value controls how much failing mail the requested policy applies to; it does not replace sender discovery or report review. A low percentage can limit exposure, but it will not reveal a sender you never found.
How long each stage should last
There is no universal waiting period. RFC 9989 describes one case explicitly: for domains that host users who may post to mailing lists and are considering p=reject, it suggests at least one month at p=none, followed by an equally long p=quarantine period. That guidance addresses the mailing-list scenario and should not be read as a rule for every domain. For other domains, the right duration depends on mail frequency, seasonal traffic, vendor changes, and your organization’s risk tolerance. A domain with a quarterly sender should be monitored across at least one of those quarters before enforcement.
Keep the provider requirement separate from your enforcement choice
Google’s sender requirements and your DMARC policy are two different decisions. Google’s email sender guidelines state that senders above 5,000 messages per day to Gmail accounts must set up SPF, DKIM, and DMARC, with the requirements applying from February 1, 2024. The same guidance permits the DMARC policy to remain p=none. Meeting the requirement means publishing and authenticating; it does not mean enforcing.
That distinction matters for planning. A domain that must publish DMARC to satisfy Gmail can stop at p=none and still be compliant with that requirement. Whether you move to quarantine or reject is your choice, based on your own inventory and risk, and it should follow the sequence above.
What each policy tag does
| Tag or value | Meaning | Rollout note |
|---|---|---|
p=none |
Requests no DMARC-specific delivery action; the record collects aggregate feedback. | Starting point for inventory and remediation. It does not block spoofed mail under DMARC. |
p=quarantine |
Requests that failing mail be treated as suspicious, which may include spam placement. | Receiver handling varies. Watch for legitimate mail in spam. |
p=reject |
Requests rejection of failing mail. | Receiver handling is guidance, and implementations can differ. |
rua |
Destination for aggregate reports. | Plan for machine parsing and high volume. |
ruf |
Destination for failure reports. | Receiver support varies; Gmail does not support it. |
pct |
Percentage of failing mail the requested policy applies to, where supported. | Provider behavior differs; do not treat it as identical at every receiver. |
sp |
Optional policy for subdomains. | Without a distinct subdomain policy, behavior can inherit from the organizational domain under DMARC rules. |
adkim and aspf |
Alignment modes for DKIM and SPF. | Relaxed is the default described by Microsoft and Google. See the alignment section. |
Choose relaxed or strict alignment deliberately
Relaxed alignment, the default in Microsoft’s and Google’s descriptions, accepts a subdomain match between the authenticated domain and the From domain. Strict alignment requires an exact domain match. Strict mode can protect a narrow domain, but it fails legitimate mail sent from a subdomain or through a third-party platform that signs with a subdomain. Before you change either mode, list the streams that use subdomains, and test the change against the reports from the next cycle. Switching to strict without that check is one of the more common causes of legitimate mail failing after enforcement.
Compare report-handling options
Report volume is the practical constraint. The table compares the three handling options on the factors that usually decide the choice. Where a value depends on your organization or on a specific vendor, it is marked as not stated.
| Factor | Dedicated mailbox or group | Internal parser | Third-party report service |
|---|---|---|---|
| Setup effort | Low: create the mailbox and publish rua |
Moderate: build or adopt an XML parser and storage | Low to moderate: onboarding and DNS changes; not stated for a specific provider |
| Data visibility | Raw XML only unless you parse it | Full, under your control | Depends on the provider’s dashboards and retention; not stated here |
| Ongoing workload | High if volume is large and nobody owns the parsing | Shifts workload to whoever maintains the parser | Lower internal workload; vendor handling must be verified |
| Cost | Staff time | Staff time and infrastructure | Subscription or usage fees; pricing not verified for any specific vendor |
If your team lacks the capacity to parse XML reports every week, a specialist report-processing service can reduce the manual work. Before you send your domain’s report data to any third party, confirm its data handling, retention, and the cost model in its own documentation.
Troubleshooting branches during rollout
- A known vendor fails after a DNS change. Confirm the record still includes the vendor’s SPF include or IP ranges and that the record count is within SPF limits. Then check that the DKIM selector still resolves.
- An unknown source sends a small volume. Investigate the source’s IP and envelope domain before concluding anything. An unfamiliar but authorized service is more common than a deliberate campaign, but you cannot tell from the report alone.
- Legitimate mail reaches spam after a stage increase. Return to the previous
pctor policy, check which stream is affected, and fix its alignment before increasing again. - Reports stop arriving. Check the record syntax, confirm the destination’s authorization record if it is external, and confirm the reporting mailbox accepts the messages.
Where the sequence leads
A working rollout starts with inventory, moves through aligned authentication and monitoring, and reaches enforcement only when the reports show that every legitimate stream passes. The policy tag is the last step in that process, not the first.
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