Red Sift’s definitive guide to email security
Last updated: November 2025
TL;DR
This comprehensive guide covers email authentication protocols (SPF, DKIM, DMARC, MTA-STS) essential for protecting domains from spoofing and phishing in 2026.
Key takeaways:
- Email remains vulnerable: 3.4 billion phishing emails sent daily, with email being the primary attack vector for cybercriminals
- SPF and DKIM alone aren't enough: They authenticate senders but don't prevent exact domain impersonation
- DMARC is now mandatory: Required by Google, Yahoo, and Microsoft for bulk senders (5,000+ emails/day) as of 2024-2025, now standard in 2026
- Implementation timeline: Red Sift OnDMARC helps organizations reach p=reject enforcement in 6-8 weeks (fastest in industry)
- Business benefits: Stops phishing, protects brand reputation, improves deliverability, enables BIMI, supports compliance (NIS2, DORA, PCI DSS, GDPR)
- Technical challenges solved: Dynamic SPF eliminates the 10-lookup limit, automated tools accelerate troubleshooting
- MTA-STS adds transport security: Encrypts email in transit between mail servers
Bottom line: Email authentication has moved from optional to required in 2026. Organizations need DMARC at p=reject for complete protection, with modern platforms enabling rapid, safe implementation.
What is this email security guide & why does email security matter?
Email is a vital tool for the lifeblood of business communication all around the world. It’s so critical to the everyday running of organizations big and small, that many would agree it’s just as essential a service as electricity or water.
But its importance is exactly what makes email vulnerable from a cybersecurity perspective. In 2026, attackers continue to refine their methods. With 3.4 billion phishing emails sent every day, it's evident that email systems are the prime target for cybercriminals seeking access to your business. All it takes is a single employee to fall victim to a socially engineered scam, click on an infected link, or download a malicious attachment, and your entire operation could grind to a halt.
Given how important it is for organizations to secure their email, we’ve developed this comprehensive guide to help both beginners and buyers with their email security related queries. In the following chapters, you’ll find in-depth information on:
- How attackers exploit weak gateways, misconfigured DNS records, and unmonitored domains
- Why SPF, DKIM, and DMARC work best together, and how MTA-STS strengthens transport security
- The buyer checklist: reporting depth, automation, policy enforcement, ROI, and time to value
Happy reading!
If you're an email security architect or an analyst looking for a more technical guide, visit our Technical Email Configuration Guide. This comprehensive handbook explores SPF, DKIM, DMARC, MTA-STS, and more, offering insights and practical tips for enhancing your email security posture.
Frequently asked questions: Email security guide
All email security measures (apart from DMARC) are ineffective at spotting a malicious email when it appears to come from a legitimate domain. This is because of a flaw in Simple Mail Transfer Protocol (SMTP). In October 2008, the Network Working Group officially labelled it 'inherently insecure', stating that anyone could impersonate a domain and use it to send fraudulent emails pretending to be the domain owner.
Anyone with a very basic knowledge of coding can learn the steps required to impersonate someone's email identity through a quick Google search. The result is an email that looks legitimate without typical phishing indicators. With 3.4 billion phishing emails sent every day, email systems remain the prime target for cybercriminals.
SPF (Sender Policy Framework) verifies that an email is sent from an IP address authorised by the sending domain's SPF record through a DNS TXT record listing authorised mail servers.
DKIM (DomainKeys Identified Mail) uses a cryptographic signature, validated via a public key in DNS, to confirm that the email's content hasn't been altered and comes from an authorised domain. Both are essential to email security, but neither prevents exact impersonation.
While the protocols tell the recipient who the email is from, the recipient has no instruction to act on this knowledge. Major inbox providers now require SPF and DKIM for bulk email senders in 2026.
DMARC stands for Domain-based Message Authentication, Reporting, and Conformance. It's an outbound email security protocol that allows domain owners to tell receiving inboxes to reject spoof emails. DMARC works by combining the results of SPF and DKIM to determine if your email is authentic and authorised.
The DMARC policy (defined by the "p=" tag in your DNS record) then tells recipient servers what to do with it. DMARC stops exact domain impersonation by instructing recipient servers not to accept any emails which aren't authenticated. In 2026, DMARC has become a standard requirement for organisations sending bulk email.
The SPF specification limits DNS lookups to 10. If your SPF record exceeds this, SPF will fail. The SPF mechanisms counted are: a, ptr, mx, include, redirect and exists. In reality, 10 lookups aren't enough because most businesses use multiple email-sending tools.
G Suite alone takes up 4 DNS lookups, add in HubSpot for marketing which uses 7 lookups and you're already over the limit. As soon as you go over 10 SPF lookups, your email traffic will begin to randomly fail validation. This is why organisations in 2026 are shifting to dynamic SPF management rather than trying to manually maintain flattened records.
Mail Transfer Agent Strict Transport Security (MTA-STS) is a standard that enables the encryption of messages being sent between two mail servers. It specifies that emails can only be sent over a Transport Layer Security (TLS) encrypted connection which prevents interception by cybercriminals. SMTP alone does not provide security, making it vulnerable to man-in-the-middle attacks where communication is intercepted and possibly changed.
Additionally, encryption is optional in SMTP, meaning emails can be sent in plaintext. Without MTA-STS, an attacker can intercept the communication and force the message to be sent in plain text. In 2026, MTA-STS has become a standard security control for organisations handling sensitive communications.
By implementing DMARC you benefit from stopping phishing attempts that appear to come from you, stronger customer trust, reduced cyber risk and compliance with bulk sender requirements from Google, Yahoo and Microsoft.
DMARC strengthens compliance with PCI DSS 4.0 and enhances overall organisational resilience against evolving cyber threats. Once at p=reject (enforcement), DMARC blocks vendor fraud, account takeovers, and email spoofing by stopping bad actors from using your domain to send phishing emails and carry out Business Email Compromise (BEC). According to Verizon's 2025 Data Breach Investigations Report, BEC attacks constitute more than 17-22% of all Social Engineering incidents.
Red Sift OnDMARC accelerates the DMARC journey with automated sender discovery, prescriptive fixes, anomaly detection, and role-based access for global teams. By 2026, leading platforms enable enterprises to reach p=reject enforcement in 6-8 weeks rather than the six month timelines once typical.
One of the most commonly reported benefits of OnDMARC is an average time of 6-8 weeks to reach full enforcement. The platform's powerful automation continuously analyses what's going on across your domain, surfacing alerts for where and how to make necessary changes. Within 24 hours of adding your unique DMARC record to DNS, OnDMARC begins to analyse and display DMARC reports in clear dashboards.
Major email providers including Microsoft, Google, and Yahoo now mandate DMARC for bulk senders (organisations sending 5,000+ emails per day) as of 2024-2025, and these requirements have become standard in 2026.
Beyond inbox provider requirements, certain industries and government regulations are moving toward mandating DMARC. U.S. federal agencies are required to use DMARC, as are DORA regulated payment processors. Additionally, DMARC implementation strengthens compliance with regulations including PCI DSS 4.0, GDPR, and NIS2. For cybersecurity, email security and IT teams, ensuring your organisation's email security aligns with international best practices and requirements is essential.