DMARC Explained: Enhancing Email Security and Preventing Spoofing

 DMARC

Domain-based Message Authentication, Reporting, and Conformance (DMARC) is an email security protocol that helps protect users from forged emails and email spoofing:

How it works

DMARC builds on the Domain Name System (DNS), DomainKeys Identified Mail (DKIM), and Sender Policy Framework (SPF) protocols to verify email senders. DMARC policies tell receiving email servers what to do with messages that don't pass these authentication checks.

What it does

DMARC helps prevent email spoofing, which occurs when attackers use an organization's domain to impersonate its employees. DMARC can also help protect a brand's reputation by blocking spoofed messages.

How to set it up

Administrators set up DMARC after SPF and DKIM. DMARC records are published as text (TXT) resource records (RR) in the sending organization's DNS database.

How to use it

DMARC policies can specify what to do with messages that fail authentication, such as moving them to the recipient's spam folder. It's recommended to start by quarantining a small percentage of emails that fail DMARC and increase over time.

This is covered in CompTIA A+, CySA+, and Security+.

 SPF (Sender Policy Framework)

Sender Policy Framework (SPF) is an email authentication protocol that verifies if an email is from an authorized server for a specific domain:

How it works

When receiving an email, the mail server checks the domain's IP address against the authorized servers listed in the SPF record. If the email is from an authorized server, it passes SPF authentication and is delivered. If the email is from an unauthorized server, it fails SPF authentication and is rejected or sent to spam.

Benefits

SPF helps protect domains from being misused by malicious actors who send spam or phishing emails. It also improves a domain's reputation and email deliverability.

Implementation

Domain owners publish an SPF record in the DNS for each domain or host with an A or MX record. SPF records are TXT files that can't exceed 10 tags or 255 characters.

DNS Record Types to know for the exam

 DNS RECORD TYPES

Make sure you know the following DNA record types for this exam and how they are used:

A: host (IPv4). Maps the name to an IPv4 address.

AAAA: host (IPv6) Maps the name to an IPv6 address.

CNAME: (Canonical Name): Alias. Example: Sites that use www as the hostname of a web server might internally call it something else, such as Dallwebserver1.

MX: Mail Exchanger. This is used for an email server.

NS: Name Server. Provides a list of the authoritative DNS servers responsible for the domain you are trying to query.

PTR: Pointer. This is a reverse record; it resolves IPv4 or IPv6 addresses to domain names.

SOA: Start of Authority. Keeps track of all of the DNS changes to help with replication.

TXT: Text. Stores descriptive information about the domain in a text format. 

SPF stands for Sender Policy Framework. It helps prevent spammers from sending emails from your domain using the email addresses of your email servers.