How to discover source owners using the ‘envelope_to’ domain?
An envelope_to domain is the domain of the recipient’s email address. So, if we shoot an email to someone@sample.com, then sample.com is the envelope_to domain. Now, let’s quickly recall what RUA reports are to understand the concept fully. So, RUA or aggregate DMARC reports are XML-based reports that are sent by the receiving server to the email address specified in the DMARC policy. It includes details like-
- The source IP addresses of senders using the domain
- Authentication results for SPF and DKIM
- The volume of emails processed
- Actions taken (e.g., none, quarantine, reject)
RUA reports help domain owners monitor email authentication performance, detect unauthorized senders, and improve email security.
Identifying the envelope_to domain and searching logs
The envelope_to domain can be used to know why some of the legitimate emails are getting flagged by DMARC. This technique is all the more useful when troubleshooting methods are somewhat questionable. You can know which vendors are sending emails on your behalf and to whom. The envelope_to domain can also be used to trace incoming emails in your logs. For example, searching with the envelope_to domain in your inbound logs can reveal which person or team in your company is using a source.
How to compare with internal records?
By thoroughly matching the sending sources with internal records, you can confirm legitimate email traffic, detect misconfigurations, and identify unauthorized email usage before it becomes a security risk.
Here’s how you can compare-
Check against the list of approved vendors
If you have officially allowed a third-party service (like a marketing platform or CRM tool) to send emails on your behalf, then check if their sending sources align with your records. If they aren’t aligning, investigate further.
Verify internal email infrastructure
Cross-check the sending sources (IPs, domains) with your organization’s email gateways, servers, and internal applications. If an email claims to be from an internal department but originates from an unknown server, it may indicate spoofing or misconfiguration.
Correlate with employees or team activity
If an email is sent from your domain but the source isn’t authorized, check with your internal team. Such sources could be used by unauthorized or ex-employees. In some cases, it could be a misconfigured application that is sending these emails unintentionally.
Detect shadow IT or unauthorized email services
Often, employees use tools that aren’t officially allowed by the company— this practice is called shadow IT. If you see an unexpected source in DMARC reports, it might be a sign of shadow IT.
Why is it important to discover source owners?
With so many email-based fraudulent activities being reported each day, you, as a brand owner, can’t ignore email security. Unguarded incoming and outgoing emails are security vulnerabilities that threat actors are always on the hunt for. By leveraging DMARC reports, you can discover both legitimate and illegitimate sources sending emails from your official domain, ensuring proper email authentication under SPF, DKIM, and DMARC.
Here’s why this security exercise matters so much-
Strengthening email security
If an unapproved sender is detected during the source investigation, then it means there is some misconfiguration or a security gap that needs immediate attention. If you regularly monitor RUA reports and match sources, then the effectiveness of SPF, DKIM, and DMARC increases, marching them to their full potential in reducing security breaches through outgoing emails.
This ultimately prevents phishing and spoofing done by impersonating your domain to deceive recipients. What else it does is let you know if your DMARC policy needs any adjustments or if your DMARC structure is ready for the strictest policy, that is, p=reject.
If you detect anomalies that indicate a phishing attempt, then tracing them back to the source helps prevent bigger damage. This ultimately secures your overall email ecosystem.
Ensuring proper email authentication
SPF, DKIM, and DMARC are the core email authentication protocols that work by relying on accurate sender identification. When unauthorized sources send emails from your domain, they fail SPF and DKIM checks. Such emails are treated as per the DMARC policy you specified. If you specify p=none, then no action is taken against such emails. But with p=quarantine, these are sent to the spam folder, while with p=reject, these are stopped from entering the recipients’ mailboxes. This also helps improve email deliverability, which is important for successful email marketing campaigns.
Staying compliant with industry standards
Many industries require organizations to comply with email security standards (e.g., GDPR, DORA). DMARC enforcement helps prevent brand abuse, ensuring that only approved sources can send emails on behalf of your domain.
Failing to comply with these standards leads to severe legal, financial, and reputational consequences for companies. If you fail to comply with GDPR, then you can be subjected to fines of up to €20 million or 4% of annual global revenue, whichever is higher, for non-compliance, especially if a data breach exposes personal information.
Moreover, a data breach due to weak email security can erode trust, leading to customer churn and reputational damage.
In conclusion, DMARC is not a one-time job; you have to monitor the reports regularly and detect anomalies to prevent abuse of your domain.