Dmarc2logstash

DMARC, which stands for “Domain-based Message Authentication, Reporting & Conformance”, is an email authentication, policy, and reporting protocol. It builds on the widely deployed SPF and DKIM protocols, adding linkage to the author (“From:”) domain name, published policies for recipient handling of authentication failures, and reporting from receivers to senders, to improve and monitor protection of the domain from fraudulent email.

Design

Monitors a given POP3 account for incoming emails and for any attachment it finds, the attachment will analyzed for DMARC XML content. If an eligible attachment, the XML is converted to JSON and written to a dmarc.log file in the current directory (/opt/dmarc2logstash/dmarc.log)If the attachment has a content type of 'application/gzip' or has a .gz or .gzip extension, then the attachment will be gunzipped before analyzing for XML content.

Why is DMARC important?

With the rise of the social internet and the ubiquity of e-commerce, spammers and phishers have a tremendous financial incentive to compromise user accounts, enabling theft of passwords, bank accounts, credit cards, and more. Email is easy to spoof and criminals have found spoofing to be a proven way to exploit user trust of well-known brands. Simply inserting the logo of a well known brand into an email gives it instant legitimacy with many users.

Users can’t tell a real message from a fake one, and large mailbox providers have to make very difficult (and frequently incorrect) choices about which messages to deliver and which ones might harm users. Senders remain largely unaware of problems with their authentication practices because there’s no scalable way for them to indicate they want feedback and where it should be sent. Those attempting new SPF and DKIM deployment proceed very slowly and cautiously because the lack of feedback also means they have no good way to monitor progress and debug problems.

DMARC addresses these issues, helping email senders and receivers work together to better secure emails, protecting users and brands from painfully costly abuse.

Why is DMARC needed?

End users and companies all suffer from the high volume of spam and phishing on the Internet. Over the years several methods have been introduced to try and identify when mail from (for example) IRS.GOV really is, or really isn’t coming from the IRS. However:

  • These mechanisms all work in isolation from each other
  • Each receiver makes unique decisions about how to evaluate the results
  • The legitimate domain owner (e.g. IRS) never gets any feedback

DMARC attempts to address this by providing coordinated, tested methods for:

Domain owners to:

  • Signal that they are using email authentication (SPF, DKIM)
  • Provide an email address to gather feedback about messages using their domain – legitimate or not
    A policy to apply to messages that fail authentication (report, quarantine, reject)
  • Email receivers to:
    Be certain a given sending domain is using email authentication
  • Consistently evaluate SPF and DKIM along with what the end user sees in their inbox
  • Determine the domain owner’s preference (report, quarantine or reject) for messages that do not pass authentication checks
  • Provide the domain owner with feedback about messages using their domain

A domain owner who has deployed email authentication can begin using DMARC in “monitor mode” to collect data from participating receivers. As the data shows that their legitimate traffic is passing authentication checks, they can change their policy to request that failing messages be quarantined. As they grow confident that no legitimate messages are being incorrectly quarantined, they can move to a “reject” policy.

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