Mailgun Email Authentication Guide

Before you start

• You need access to the DNS settings for your domain. This is usually at your domain registrar or DNS provider (Cloudflare, Namecheap, GoDaddy, etc.).
• You need admin or settings access to your Mailgun account to generate DKIM keys and verify records.
• DNS changes take time to propagate. After saving a record, wait at least 15-30 minutes before testing.

SPF Setup for Mailgun

SPF (Sender Policy Framework) is a DNS TXT record that lists which mail servers are allowed to send email on behalf of your domain. Receiving servers check it to decide whether to accept or flag your mail.

Mailgun provides the exact DNS records for your domain in the DNS Records tab. Copy the SPF value from there rather than using a generic include.

SPF record for Mailgun

Type: TXT    Host/Name: @    Value: v=spf1 include:mailgun.org ~all

Steps

1. Open your DNS provider and look for an existing TXT record at host @ that starts with v=spf1.
2. If one exists, edit it and add the new include. Never create a second SPF record. If none exists, create a new TXT record at @ with the value above.
3. If you send through both Mailgun and Google Workspace, combine them: v=spf1 include:mailgun.org include:_spf.google.com ~all
4. Use ~all (softfail) while testing. Move to -all (hardfail) only after confirming all legitimate senders are covered.
5. Save and wait for DNS propagation.

DKIM Setup for Mailgun

DKIM (DomainKeys Identified Mail) adds a cryptographic signature to outgoing email. Receiving servers verify the signature against a public key you publish as a DNS TXT record. A valid DKIM signature proves the message was not altered in transit and that it came from an authorized sender.

Selector for Mailgun: shown in your Mailgun DNS Records tab (often mailo or pic)

Steps

1. In Mailgun, go to Sending → Domains → select your domain → DNS Records tab.
2. Mailgun shows you the exact TXT or CNAME record for DKIM. Copy the host name and value exactly.
3. Create the record in your DNS provider. The host will be something like mailo._domainkey.
4. Return to Mailgun and click "Check DNS Records Now". The green checkmark confirms DKIM is verified.

Verify DKIM

• Send a test email to a Gmail address and open it. Click the three-dot menu → "Show original". Look for dkim=pass in the authentication results.
• From the command line:
  

  dig TXT selector._domainkey.yourdomain.com +short

• Or use the InboxGreen DKIM checker.

DMARC Setup for Mailgun

DMARC (Domain-based Message Authentication, Reporting, and Conformance) ties SPF and DKIM together. It tells receiving servers what to do with mail that fails both checks, and sends you reports about who is sending email on behalf of your domain. DMARC also requires alignment: the domain in your visible From header must match the domain authenticated by SPF or DKIM.

Mailgun's domain authentication sets up DKIM alignment. Verify your sending domain in Mailgun matches the From header domain before moving DMARC beyond p=none.

The three-stage approach

Stage	DNS value	When to use it
Monitor	v=DMARC1; p=none; rua=mailto:[email protected]; fo=1	Start here. Collects reports without blocking any mail.
Quarantine	v=DMARC1; p=quarantine; pct=25; rua=mailto:[email protected]; fo=1	After 2-4 weeks at p=none with clean reports. Sends some failing mail to spam.
Reject	v=DMARC1; p=reject; pct=100; rua=mailto:[email protected]; fo=1	Full protection once SPF and DKIM alignment is verified.

Publish the DMARC record

1. Create a TXT record at host _dmarc (not @) with the p=none value above.
2. Replace [email protected] with a real inbox that can receive XML report emails.
3. Wait for DNS propagation, then verify with dig TXT _dmarc.yourdomain.com +short.
4. After 2-4 weeks, review the reports and tighten the policy when alignment looks healthy.

List-Unsubscribe for Mailgun

The List-Unsubscribe header gives inbox providers like Gmail and Outlook a machine-readable way to offer a one-click unsubscribe button. When it is present and valid, Gmail shows an "Unsubscribe" link next to the sender name without the recipient needing to scroll to the bottom of the email. This reduces spam complaints and protects your sender reputation.

How to enable it

1. In your sending platform or email template, enable the List-Unsubscribe header option. Most platforms (SendGrid, Mailgun, Brevo, Shopify Email) have a toggle or a macro for this.
2. Use a one-click HTTPS unsubscribe URL as the primary method. Include a mailto: address as fallback.
3. Add the List-Unsubscribe-Post header to declare one-click support (required by Gmail's February 2024 guidelines for senders above 5,000 messages/day).

Example headers

List-Unsubscribe: <https://yourdomain.com/unsubscribe/TOKEN>, <mailto:[email protected]?subject=unsubscribe>
List-Unsubscribe-Post: List-Unsubscribe=One-Click

Common mistakes

• Using a broken or expired token in the unsubscribe URL. Inbox providers test the link periodically.
• Only providing a mailto: link without a one-click HTTPS URL. Gmail and Outlook prefer the HTTPS method.
• Not honoring the unsubscribe request immediately. Gmail requires that one-click unsubscribes are processed within two business days.

To verify, send a test email to a Gmail address and look at "Show original". You should see the List-Unsubscribe header in the raw message headers.

Verify All Four Records

After publishing all records, run these checks:

Record	Command	What to look for
SPF	dig TXT yourdomain.com +short	One TXT record starting with v=spf1
DKIM	dig TXT selector._domainkey.yourdomain.com +short	A TXT record starting with v=DKIM1
DMARC	dig TXT _dmarc.yourdomain.com +short	A TXT record starting with v=DMARC1
All three	InboxGreen Free Check	Green pass on SPF, DKIM, and DMARC

Common Mistakes with Mailgun

• Guessing or copying DKIM values from the internet instead of using the exact records from the Mailgun DNS Records tab.
• Using the wrong record type: Mailgun provides TXT on some plans and CNAME on others. Check your DNS Records tab.
• Forgetting to merge SPF includes when sending from Mailgun alongside another provider.

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