February 22, 2025
O. Wolfson
Email is a foundational technology of the internet, enabling asynchronous communication between individuals and organizations. Behind every email sent or received is a complex system of protocols, authentication mechanisms, and network configurations that ensure secure and reliable delivery.
This guide provides a comprehensive technical overview of email systems, covering core email protocols, DNS configurations, authentication methods, and best practices for managing email services.
To fully grasp the concepts in this guide, readers should have a basic understanding of:
If these concepts are new to you, a brief review of networking basics will be helpful before diving into the details of email systems.
SMTP is the protocol responsible for sending emails between mail servers and clients.
IMAP allows users to access and manage emails stored on a remote mail server.
POP3 is used to download emails from the server to a local device.
The Domain Name System (DNS) plays a crucial role in email delivery, authentication, and security. Email systems rely on specific DNS records to determine where to send emails, verify sender authenticity, and prevent fraudulent messages from reaching users. Configuring these records correctly helps improve email deliverability, mitigate spam, and enhance security.
This section explores four key DNS records used in email communication: MX (Mail Exchange), SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting, and Conformance). Each serves a specific function in the email authentication ecosystem.
MX records specify which mail servers are responsible for receiving email on behalf of a domain. When an email is sent to an address under a particular domain (e.g., user@example.com), the recipient’s email provider checks the domain’s MX records to determine where to route the email.
example.com. IN MX 10 mail.example.com.
example.com. IN MX 20 backup.example.com.
This configuration directs email to mail.example.com first and uses backup.example.com as a fallback.
SPF helps prevent email spoofing by specifying which mail servers are authorized to send emails on behalf of a domain. It reduces spam by allowing email servers to verify whether an email claiming to come from a domain is sent from an approved source.
example.com. IN TXT "v=spf1 include:mailgun.org include:_spf.google.com ~all"
include mechanism allows third-party services (e.g., Mailgun, Google) to send emails on behalf of example.com.~all at the end signifies a soft fail for unauthorized senders (emails may be accepted but flagged).DKIM helps ensure email integrity by adding a cryptographic signature to outgoing emails. It verifies that emails were not altered during transit and confirms the authenticity of the sender.
mailo._domainkey.example.com IN TXT "v=DKIM1; k=rsa; p=MIGfMA0..."
v=DKIM1: Indicates the DKIM version.k=rsa: Specifies the encryption algorithm.p=MIGfMA0...: The public key used for email verification.DMARC builds on SPF and DKIM to enforce email authentication policies and provides reporting on unauthorized email use. It helps prevent phishing and spoofing attacks.
p=none: Monitor but take no action.p=quarantine: Send failed emails to spam.p=reject: Block failed emails completely._dmarc.example.com IN TXT "v=DMARC1; p=quarantine; rua=mailto:dmarc-reports@example.com"
p=quarantine: Sends suspicious emails to spam.rua=mailto:dmarc-reports@example.com: Email reports of authentication failures to an administrator.Used for automated emails such as password resets, order confirmations, and notifications.
Provide inboxes and full email services for personal or business use.
Allow users to forward incoming emails to another email account.
Provide SMTP servers for sending outbound emails with higher deliverability.
Understanding email protocols, DNS configurations, and security measures is essential for developers, IT admins, and businesses. Whether you're setting up a business email, automating transactional emails, or ensuring high email deliverability, mastering these concepts will enable you to operate efficiently in the technical email landscape.
For further reading, explore the official documentation of services like Mailgun, Resend, and Amazon SES, as well as IETF standards for SMTP (RFC 5321) and email authentication (RFC 7208 for SPF, RFC 6376 for DKIM, and RFC 7489 for DMARC).