Domains
Implementing DMARC
Implement DMARC to build trust in your domain and protect against email spoofing and unauthorized use of your domain in email messages.
Prerequisites
Since DMARC relies on DKIM AND SPF, first ensure your existing emails are passing SPF and DKIM.- DKIM verifies the email wasn’t altered in transit using cryptographic authentication.
- SPF authorizes IP addresses to send email for a domain.
What is DMARC?
DMARC (Domain-based Message Authentication, Reporting, and Conformance) is an email authentication protocol that instructs mail servers what to do if an email message fails SPF and DKIM, preventing email spoofing (forged headers). DMARC is added to a domain through a TXT record added to the domain at_dmarc.
By preventing spoofing, a domain can build trust with mailbox providers, as it allows them to verify that emails are authorized to send on behalf of that domain.
An email must pass either SPF or DKIM checks (but not necessarily both) to achieve DMARC compliance and be considered authenticated. A message fails DMARC if both SPF and DKIM fail on the message.
Implementing DMARC
1. Add a TXT _dmarc Record
To start, add a flexible DMARC record to your domain.
| Name | Type | Value |
|---|---|---|
| _dmarc.example.com | TXT | v=DMARC1; p=none; rua=mailto:dmarcreports@yourdomain.com; |
v- Version: This is the version of DMARCp- Policy: This is telling the inbox how to process messages that fail DMARC. Options arenone,quarantine,reject. It’s a best practice to usequarantineorreject, but you should only do it once you know your messages are delivering and fully passing DMARC.rua- Reporting URI of Aggregate: Provide a valid address that can receive email. The address can be a different domain than the one on which you set the DMARC policy. The aggregate report comes as an email with a.xmlfile attached that shares the IP sources of your messages and if they passed SPF or DKIM.
p=none; before moving to a stricter policy.
2. Test to Confirm Delivery and Passing
To test emails, send an email from all the applications and services your domain uses. Confirm that the messages are delivered to the inbox and that the headers show DMARC passing. Spending a few at this step is a good rule of thumb to ensure you’re checking all sources of email from your domain and catch email that is sent at a different cadence than daily. To confirm DMARC passed, you can inspect the email headers and confirm there isdmarc=pass.
Gradually identify email sources using tools like Google Postmaster
Tools, which provides DKIM/SPF feedback.
DMARC monitoring
services can aggregate
your email sources by collecting DMARC reports, helping you discover any
services sending email on your domain’s behalf.
3. Upgrade Policy
Once you have verified DMARC is passing across all your sending, you should upgrade your Policy top=quarantine;. This policy gives mailbox providers greater confidence in your domain since your domain only allows authenticated email.
| Policy | Value |
|---|---|
| p=none; | Allow all email. Monitoring for DMARC failures. |
| p=quarantine; | Send messages that fail DMARC to the spam folder |
| p=reject; | Bounce delivery of emails that fail DMARC. |
p=quarantine; or p=reject; you can explore setting up BIMI, which can provide established brands even greater sending credibility by displaying a logo as an avatar in an email client.
Reference
While the DMARC protocol includes both
pct and ruf parameters, they are
not widely followed by mailbox providers. These settings may not be respected
or followed.| Parameter | Purpose | Example |
|---|---|---|
v | Protocol version | v=DMARC1 |
pct | Percentage of messages subjected to filtering | pct=20 |
ruf | Reporting URI for forensic reports | ruf=mailto:authfail@example.com |
rua | Reporting URI of aggregate reports | rua=mailto:aggrep@example.com |
p | Policy for organizational domain | p=quarantine |
sp | Policy for subdomains of the OD | sp=reject |
adkim | Alignment mode for DKIM | adkim=s |
aspf | Alignment mode for SPF | aspf=r |
Having issues setting up DMARC? We can help.