Send Spoofers Packing: Master DMARC for Sendinblue and Email Deliverability

Is your domain being impersonated? Are critical emails ending up in spam folders? Following this definitive guide to Sendinblue DMARC and deliverability sets you on the path to inbox success.

Implement robust email authentication to build sender reputation, stop spoofing, and bypass filters so customers open every legitimate message.

Page Contents

Understanding DMARC and Its Importance for Email Deliverability

Email is a critical communication channel for businesses today. However, with the rise of spam, phishing, and spoofing attacks, deliverability has become a major concern. This is where DMARC comes in.

What is DMARC and How Does it Work?

DMARC stands for Domain-based Message Authentication, Reporting, and Conformance. It is an email authentication protocol that allows domain owners to specify policies for email sent from their domain.

Here’s a quick overview of how DMARC works:

  • It builds on top of two other authentication mechanisms – SPF and DKIM.
  • SPF verifies that the sending server is authorized to send emails from your domain.
  • DKIM cryptographically validates that the contents of the email have not been tampered with.
  • DMARC uses the results of SPF and DKIM checks to determine if an email should be accepted, rejected, or quarantined.
  • Domain owners configure a DMARC DNS TXT record with their policy – none, quarantine, or reject.
  • Receiving mail servers check published DMARC records and apply the specified policy.
  • Aggregate and forensic reports provide visibility into email streams.

For example, a bank can set a DMARC policy to reject emails failing SPF or DKIM. This will prevent spoofing attacks trying to impersonate the bank’s domain.

The Benefits of Implementing DMARC for Your Domain

Here are some key benefits of adding DMARC protection for your domain:

  • Prevents spoofing and phishing: DMARC rejects spoofed or fraudulent emails sent from your domain. This protects your brand reputation.
  • Improves deliverability: Emails that pass DMARC are more trusted by receiving servers and less likely to be flagged as spam.
  • Actionable reporting: DMARC aggregate and forensic reports provide deep insights into your email sources, authentication, and threats.
  • Flexibility: DMARC allows a gradual rollout, starting with monitoring before enforcing strict policies.
  • Industry best practice: DMARC is recommended and adopted by leading email providers like Gmail, Outlook, Yahoo.

How DMARC Authentication Improves Email Deliverability

Enforcing DMARC provides receiving mail servers confidence that your emails are genuinely from you. Here’s how it helps deliverability:

  • Builds sender reputation: DMARC alignment indicates your domain has good authentication practices.
  • Fewer spam complaints: Spoofed phishing emails are blocked, reducing spam complaints associated with your domain.
  • Bypasses filters: Emails meeting DMARC policies reliably bypass spam filters and reach the inbox.
  • Trusted by ISPs: Major ISPs like Gmail trust domains with DMARC, improving your sender rating with them.
  • Safeguards IP reputation: DMARC prevents spammers from damaging your IP reputation by sending spoofed spam.
  • Investigates issues: DMARC reports highlight authentication issues impacting deliverability.

Gradually implementing stricter DMARC policies ensures you maintain deliverability. Starting in monitor mode allows you to identify and authenticate all legitimate email sources before taking action. Advanced policies like percentage-based ramp-up give you greater control.

With DMARC in place, recipients and ISPs can trust that emails from your domain are genuine. This results in higher inbox placement rates and lower spam folder deliveries. For any business relying on email marketing, communications, and notifications, improving deliverability through DMARC is essential.

Setting up DMARC for Sendinblue

Sendinblue is a popular email marketing and transactional email service. To leverage DMARC for better deliverability, you need to configure Sendinblue’s authentication protocols. This involves enabling DKIM signing and publishing public keys.

Enabling DKIM Signing for Your Sendinblue Domain

DKIM or DomainKeys Identified Mail adds a digital signature to outbound emails. This allows recipients to verify the email’s authenticity.

Here are the steps to enable DKIM signing in Sendinblue for your custom domain:

  1. Login to your Sendinblue account and go to the Domains page.
  2. Click Verify next to the domain you want to configure.
  3. Check the box for “I would like to use this domain name to sign my emails”.
  4. Enter your custom signing domain, for example
  5. Click Save. Sendinblue will display the DNS entries needed.

Sendinblue signs emails on your behalf by default. The steps above allow using your own domain for signing instead. This is recommended, as it allows DMARC alignment.

Publishing Your Sendinblue DKIM Public Key in DNS

After getting the DKIM DNS records from Sendinblue, you need to publish them in your domain’s DNS for public validation.

The DKIM record will look like this: IN TXT "k=rsa; p=...."

To publish it:

  1. Login to your domain registrar or DNS hosting provider.
  2. Create a new TXT record.
  3. Enter the hostname copied from Sendinblue, e.g. mail._domainkey.
  4. Paste the TXT value provided by Sendinblue.
  5. Save the record and allow up to 48 hours for propagation.

Once propagated, DKIM signing using your domain will be active.

Configuring SPF for Sendinblue DMARC Compliance

To fully align with DMARC, SPF is also required. SPF confirms Sendinblue’s servers are permitted to send mail on behalf of your domain.

Since Sendinblue doesn’t allow configuring a custom SPF record, you have two options:

  1. Use a dedicated IP: Sendinblue provides dedicated IPs for sending which can be added to your SPF record.
  2. Set a Return-Path: Configure Sendinblue to set a custom Return-Path (also called MAIL FROM domain). This bypasses the SPF check.

For example, you can set a Return-Path like which matches your sending domain.

To set a custom Return-Path domain in Sendinblue:

  1. Go to Account > Senders & IPs
  2. Under “Define Return-Path domain”, add your custom domain.
  3. Allow up to 48 hours for changes.

With both DKIM and a Return-Path set, Sendinblue can fully align with your DMARC policy. Make sure to verify alignment using a DNS lookup tool before enforcing DMARC rejects.

With these steps complete, your Sendinblue configuration will be DMARC compliant. Emails sent will be authenticated, improving deliverability and protecting your domain from spoofing.

Advancing Your DMARC Policy to Reject or Quarantine

Once your domain is DMARC compliant, you can start enforcing stricter policies to block invalid emails. This involves gradually advancing from monitoring to quarantine and reject.

Starting with a DMARC Record in Monitoring Mode

It’s recommended to start by deploying a DMARC record in “monitor-only” mode. This allows you to collect authentication data without impacting mail flow.

A monitor DMARC record looks like: TXT "v=DMARC1; p=none; rua=mailto:[email protected]"

With p=none, emails that fail alignment are still delivered. But you’ll receive aggregate reports about compliance.

This serves two purposes:

  • Identifies legitimate email sources that need DMARC alignment.
  • Highlights fraudulent emails impersonating your domain.

Analyzing reports in monitoring mode allows you to authenticate all your email streams before taking action. Look for sources with high volumes of failed messages, and work to align them.

Once you’ve aligned or eliminated unnecessary sources, you can start tightening policies.

Moving From Monitoring to Quarantine Mode

The next phase is to tell receiving servers to send non-compliant mail to the spam folder. This is done using p=quarantine: TXT "v=DMARC1; p=quarantine; ..."

Additionally, use the Percent (pct) tag to only quarantine a portion of non-compliant mail:


Start with a small pct value like 10-25%, and gradually increase it while monitoring reports. With pct less than 100%, the rest of the emails will only be monitored and reported without action.

Quarantining allows you to slowly rollout enforcement and minimize the chance of false positives being flagged. Re-check reports for any legitimate sources unexpectedly quarantined during this phase.

Once confident, usually after a few weeks of ramp-up, you can start planning for full rejection.

Implementing a Full DMARC Reject Policy

The final step is switching to p=reject which discards invalid emails at the protocol level: TXT "v=DMARC1; p=reject; pct=100" 

With pct=100, all non-compliant emails detected are rejected. However, you should still:

  • Maintain aggregate and failure reporting to keep monitoring domain health.
  • Use ruf=forensic reporting to identify false rejections.
  • Temporarily rollback to p=quarantine if issues arise.
  • Plan response in case of incorrectly rejected legitimate mail.

Also, encourage partners and vendors sending from your domain to implement DMARC themselves. This avoids their mail being blocked by your policies.

With a full reject policy, you’ve completed DMARC implementation! Continuously monitor reports to ensure alignment and prevent new issues. Revisit policies if rejections are higher than expected.

DMARC is an ongoing process requiring vigilance as your email ecosystem evolves. But stopping impersonation and spoofing provides immense protection for your brand, customers, and partners. The effort to progressively enforce DMARC delivers long term dividends through better deliverability, security, and compliance.

Monitoring Your DMARC Reports and Logs

DMARC generates aggregate and forensic reports to help you continuously monitor the health of your email streams. Analyzing these reports is critical for identifying issues and optimizing your policies.

Understanding DMARC Aggregate and Forensic Reports

There are two main types of reports generated by DMARC:

Aggregate reports provide daily summarizations of traffic and policy actions. These include:

  • Volume numbers for total emails and failed messages.
  • Failures categorized by source and error reason.
  • Statistics on DMARC policy results like rejections.

Forensic reports contain message-level details sent in real-time as actions occur. These include:

  • Metadata like source IPs and email headers.
  • DKIM and SPF results on individual messages.
  • Policy details like reject reasons.
  • Message snippets like subject lines.

Forensic reports require more storage and processing capacity due to their size. Aggregates provide a lighter alternative for overview monitoring.

Both types of reports are essential for monitoring your DMARC deployment.

Useful Tools for Analyzing DMARC Reports

Parsing DMARC reports in raw XML is difficult. To properly analyze them, it’s recommended to use a reporting tool like:

  • DMARC Analyzer – Web reporting platform by DMARC experts dmarcian.
  • DMARC Digest – Weekly aggregate report emails by Postmark.

These tools transform hard-to-read XML into visual charts, graphs, and tables. Some provide commentary and actionable suggestions on improving alignment.

For high volumes, consider automated solutions that programmatically ingest reports and highlight important metrics. This allows you to focus on identified issues.

Key Metrics to Track in DMARC Reports

Useful statistics and metrics to monitor in reports include:

  • Authentication failures – Where emails are failing DKIM and SPF checks. Indicates alignment issues.
  • Failure rates – The percentage of failures compared to total traffic. Rising failure rates may signal problems.
  • Reject/quarantine volumes – The amount of email being rejected or quarantined by your policies. Watch for unexpected spikes.
  • Top sources – Highest volume sources can be prioritized for alignment efforts.
  • Policy overrides – Where receiver policies are not being applied, due to local policies.
  • Large receivers – Top recipient domains provide visibility into where your mail is going.
  • SMTP errors – Transport-level rejects often require investigation to diagnose root cause.
  • Threat data – Details on policy actions taken against suspicious traffic.

Tracking metrics over time reveals trends and the impact of DMARC policy changes. Share reports with departments sending from your domain to maintain alignment.

The path to effective DMARC monitoring includes:

  • Properly ingesting and analyzing report data.
  • Distilling metrics meaningful to your situation.
  • Collaborating with internal teams to continuously improve.
  • Reviewing reports as an early warning system.

With vigilance and visibility into your reports, you can remediate issues early and optimize the protection DMARC provides.

DMARC Best Practices For Maximum Email Deliverability

Properly implementing DMARC improves deliverability. However, you need to follow certain best practices to achieve maximum benefit:

Authenticating All Email Sources with DKIM and SPF

The foundation of DMARC is authenticating all your email sources with DKIM and SPF. This includes:

  • Email providers like Gmail and Office 365.
  • Marketing systems such as MailChimp, Constant Contact, Campaign Monitor.
  • CRMs including Salesforce, Zoho, and HubSpot.
  • Transactional mail services like Postmark, SendGrid, Mailgun.
  • Cloud hosting providers such as AWS SES, Google Cloud.
  • Internal on-premise mail servers.
  • Domains of acquired companies.

For each source, check if DKIM signatures and SPF records are correctly published. Monitor DMARC reports to see if additional streams need alignment.

Identify forwarded mail resulting in SPF fails, as recipients forward your mails after receipt. Consider adding common email services like Gmail, Outlook, and Yahoo to your SPF record.

Tips for managing email sources:

  • Maintain a list of all domains and IP addresses that send email from your domain.
  • Assign responsibility to technical teams for aligning and monitoring sources they manage.
  • Set a policy requiring new services to be DMARC compliant prior to use.
  • Audit internally hosted mail servers to ensure they implement SPF and DKIM.
  • Monitor traffic from sources you didn’t setup yourself, like compromised accounts.

With rigorous management of sources, you can authenticate legitimate emails and minimize DMARC failures.

Managing and Updating Your SPF Record

Your SPF record specifies all authorized sending infrastructure for your domain. Keeping it current is critical as you add or change systems.

  • Review your SPF record quarterly for accuracy.
  • Lookup IP addresses to confirm services haven’t changed mail servers.
  • Watch for peaks in traffic from unfamiliar IPs.
  • Limit use of broad SPF modifiers like
  • Adjust to a tighter -all mechanism once your record is stable.
  • Specify numerical SPF modifiers like -all:5 to favor allow over block.
  • Publish changes incrementally to avoid breaking mail flow from outdated records.

Publishing a precise SPF record prevents your security policies from unintentionally blocking valid mail.

Using Return Paths and Feedback Loops

Return Paths (also called envelope FROM) determine where bounced and undeliverable mails are sent.

  • Set a dedicated return path domain for your ESP like
  • Include this domain in your SPF record for alignment.
  • Monitor abuse reports for spoofing attempts on your return path.

Feedback loops allow ISPs to report rejected mail back to the apparent sender.

  • Support RFC 8658 SMTP feedback loop messages.
  • Analyze feedback data for DMARC rejections.
  • Inform senders (like partners) when their mail you originate is rejected by your policies.

With good return path and feedback practices, you close the loop on email authentication.

Improving Your Sender Reputation and Engagement

DMARC protects your domain’s reputation, but ongoing hygiene is still required:

  • Publish accurate contact information in WHOIS and on your website.
  • Proactively mitigate issues that trigger spam complaints.
  • Remove inactive subscriber addresses from lists.
  • Honor unsubscribe requests immediately.
  • Ensure marketing content provides value to recipients.
  • Avoid spammy patterns like overuse of ALL CAPS and exclamation points!!

Monitor sender rating services like IPQualityScore and SenderScore. Use this data to identify and improve problem areas.

Engaged recipients who open, read, and click on your emails improve deliverability. Measure engagement metrics like open, clickthrough, and response rates. Optimize content, calls to action, scheduling, and segmentation to boost engagement.

With DMARC and diligent reputation management, your emails will be welcomed by recipients and prioritized for inbox delivery.

Frequently Asked Questions About Sendinblue DMARC

When implementing DMARC with Sendinblue, you may have some common questions come up. Here are answers to a few frequently asked ones:

Does Sendinblue Support Full DMARC Compliance?

Sendinblue provides the required DKIM signing to align with DMARC policies. However, they do not allow configuring a custom SPF record.

To get full DMARC compliance with Sendinblue:

  • Enable DKIM signing using your sending domain, not their default domain.
  • Add the DKIM public key to your DNS records.
  • Obtain a dedicated IP address from Sendinblue to publish in your SPF record.
  • Or, set a custom MAIL FROM domain in Sendinblue that matches your sender domain.

With both DKIM and SPF alignment in place, Sendinblue can provide full DMARC compatibility. Validate setup using DNS lookup tools before enforcing reject policies.

What if DKIM Passes but SPF Fails for Sendinblue?

If DKIM aligns but SPF fails, it typically indicates an issue with your SPF record or configuration. Some things to check:

  • Confirm your SPF record includes Sendinblue’s dedicated IP address if used.
  • Verify the IP address mapped to Sendinblue’s servers hasn’t changed.
  • Check if you have a valid MAIL FROM domain set in your Sendinblue account.
  • Use a DNS lookup tool to see if Sendinblue is sending with your MAIL FROM domain.

If emails show your domain in the MAIL FROM, but Sendinblue’s servers are not in your SPF, the SPF check will fail. The failures would be valid and your SPF record needs updating.

However, if the MAIL FROM contains, then SPF fails are expected. This alignment issue would be resolved using a custom MAIL FROM domain.

How Long Does it Take for DNS Changes to Apply?

DNS record changes can take up to 48 hours to fully propagate across the internet. However, DNS caches will start to refresh the updated record much sooner than that.

Here are general guidelines for DNS TTLs when managing DMARC:

  • Set DMARC/DKIM/SPF TTLs lower at first, like 600 seconds.
  • Monitor reports to see if changes apply within a few hours.
  • Increase TTL gradually after confirming updates work.
  • For final DMARC policies, TTLs of 2-3 hours are common.

Some platforms like dmarcian allow you to reload records from DNS. This checks if changes are live rather than waiting full propagation times.

In most cases, you should see DMARC and other policy updates reflected in reports within 6-12 hours. Be patient and avoid continuously modifying records before prior changes take effect.

With short initial TTLs, you can deploy updates rapidly. Longer values provide better caching once your configuration is stable.

What is the difference between reject and quarantine policies?

A reject policy tells receiving servers to discard emails failing DMARC completely. Quarantine sends non-compliant emails to the spam folder instead of outright rejection. Quarantine is safer when first enforcing policies.

How do I monitor DMARC reports?

Use a reporting service like dmarcian or DMARC analyzer tools to parse aggregate and forensic XML reports into human-readable formats. Monitor failure rates, reject volumes, threats detected, and other key metrics.

What happens if DMARC blocks a legitimate email?

If an important email is rejected, temporarily rolling back your policy to p=none or p=quarantine can help while you diagnose the cause. Check forensic reports for details like headers and use rua= reports to notify the original sender.

Should DMARC reject policies be increased gradually?

It’s recommended to gradually increase rejection percentages over several weeks. Start with small pct values like 10%, monitor reports for issues, then slowly raise towards 100% to minimize unintended impacts.

How do I troubleshoot DMARC alignment issues?

If sources show high DMARC failure rates, reconfirm DKIM and SPF records are published correctly. Check any recent changes made to mailing infrastructures. Use DNS lookup tools to validate records are as expected.

What should I do if a partner/vendor has DMARC reject issues?

First check if they have their own DMARC policies causing self-rejections. If issues are from your policies, notify them to implement aligned DKIM/SPF signing to authenticate their mail. Temporarily excluding their domain can allow time to comply.

How often should I review DMARC aggregate reports?

Reviewing aggregate reports daily initially is recommended to monitor the impact of policy changes. Once stable, weekly reviews are sufficient for general domain health monitoring. Set alerts for spikes in reject/quarantine volumes.

What is the recommended DMARC record format?

Use a TXT record format for broad compatibility. For example: TXT "v=DMARC1; p=reject; pct=100; rua=mailto:[email protected]; ruf=mailto:[email protected];"

How long does DMARC record changes take to apply?

Plan for up to 48 hours for DNS changes to fully propagate globally. Start with lower TTL values like 600 seconds, monitor report changes, then increase TTL gradually for caching benefits once stable.

Key Takeaways

Implementing DMARC and improving email deliverability takes effort but provides enormous benefits for your domain’s protection and reputation. Here are the key takeaways:

  • DMARC stops spoofing and fraudulent emails by rejecting unaligned messages. This prevents phishing and scams.
  • Configuring DKIM and SPF enables DMARC authentication for your email streams. Sendinblue supports DKIM and custom return paths to align.
  • Start with monitor only mode to identify alignment issues without impacting mail flow. Then gradually increase enforcement.
  • Analyze DMARC aggregate and forensic reports to monitor your email ecosystem and fine-tune policies over time.
  • Authenticating all sources, managing SPF records, using return paths, and maintaining engagement helps maximize deliverability.
  • With rigorous DMARC practices, recipients and ISPs can trust your emails, reducing spam false positives and improving inbox placement.
  • Implementing DMARC aligns your domain with industry best practices followed by leading email providers.
  • Ongoing vigilance is required to monitor reports, optimize policies, and adapt DMARC as your email streams evolve.

With DMARC providing critical protection and deliverability gains, every brand should evaluate implementation plans. Follow the steps outlined to configure Sendinblue and your domain for success.