Technical basics of email domain security

SPF – Sender Policy Framework

SPF ensures that only authorized mail servers are allowed to send emails on behalf of your domain. Receiving systems can thus reliably verify whether an email actually originates from a legitimate source or whether the sender address has been misused.

Properly configured SPF significantly reduces the risk of sender spoofing, phishing, and fraudulent communication. At the same time, SPF protects your domain's reputation and improves the deliverability of legitimate emails.

SPF is an essential foundational technology for modern email security. For comprehensive protection, it is combined with other methods such as DKIM and DMARC to holistically secure the identity, integrity, and trustworthiness of email communication.

Tools, Policies und Zertifikate, die vor Phishing und anderen Cyberangriffen schützen

DKIM – DomainKeys Identified Mail

DKIM complements SPF by digitally signing every outgoing email. This signature allows receiving systems to uniquely verify that a message actually originates from the stated sender and that its content has remained unchanged during transmission.

DKIM protects the integrity and credibility of your email communication, prevents manipulation, and sustainably strengthens trust in your domain. In combination with SPF and DMARC, DKIM forms a central pillar of a professional and secure email infrastructure.

DMARC – Domain-based Message Authentication, Reporting and Conformance

DMARC is the overarching control level for email security. It evaluates the results of SPF and DKIM and definitively determines how receiving mail servers should handle unauthenticated emails – from normal delivery to quarantine to outright rejection.

Furthermore, DMARC provides complete transparency into email activity on behalf of your domain through comprehensive reporting capabilities. Abuse, misconfigurations, and potential attack attempts become visible and controllable. In combination with SPF and DKIM, DMARC enables effective enforcement of your email security strategy and sustainably protects your brand, reputation, and customer trust.

DNS security and DNSSEC

DNS security describes measures to protect the Domain Name System (DNS). DNSSEC (Domain Name System Security Extensions) ensures that DNS records – for example, for mail servers, SPF, DKIM, or DMARC – cannot be manipulated or falsified.

DNSSEC thus protects the integrity of the underlying infrastructure and prevents attackers from injecting false server information.

Key DNS security strategies include:

• the use of protocols such as DNSSEC for authenticating DNS data

• the implementation of DNS filters to block malicious or harmful websites

• the encryption of DNS traffic through technologies such as DNS over HTTPS (DoH)

  
  

These measures prevent attackers from:

• Redirecting users to fake websites

• steal sensitive data

• carry out further harmful or abusive activities

TLS & Cipher – Secure Data Transmission

TLS (Transport Layer Security) protects the confidentiality and integrity of data transmission between systems. Crucially, this requires not only the activation of TLS, but also the use of secure and up-to-date encryption methods (cipher suites).

Outdated TLS versions or insecure ciphers allow

· Eavesdropping,

Manipulation and

Downgrade attacks, especially in email communication.

A professional configuration ensures that only strong TLS versions and modern ciphers are used.

In combination with MTA-STS and DANE, encryption is enforced and protected against man-in-the-middle attacks. Correctly implemented TLS reduces data protection, compliance, and liability risks and strengthens trust in the company's digital communication.

 

BIMI – Brand Indicators for Message Identification

BIMI enables the display of a verified brand logo in the email inbox. Requirements are:

• a strict DMARC policy

• a trademarked logo

• a Verified Mark Certificate (VMC)

BIMI strengthens the trust of recipients and makes phishing attacks more difficult, as only correctly authenticated senders can display their logo.

MTA-STS – Mail Transfer Agent Strict Transport Security

MTA-STS (Mail Transfer Agent – Strict Transport Security) enforces the use of encrypted TLS connections when receiving emails.

This ensures that:

• Emails will only be transmitted in encrypted form.

• Manipulations through downgrade attacks are prevented.

• attackers cannot insert themselves undetected between the mail servers.

MTA-STS complements STARTTLS by mandating encryption and requiring verifiable certificate validation. This enables a sustainable and reliable increase in the transport security of emails.

 

DANE – DNS-based Authentication of Named Entities

DANE (DNS-based Authentication of Named Entities) links TLS certificates directly to secure DNS entries.

In combination with DNSSEC, DANE ensures that mail servers only accept trusted and verified certificates . This effectively protects email transport against man-in-the-middle attacks and certificate manipulation .

DANE thus increases the reliability of encrypted connections and strengthens the integrity of all email communication.