Email is the single most exploited attack surface in business today. Phishing attacks account for the majority of data breaches, business email compromise costs organizations billions each year, and ransomware most commonly arrives through a malicious email attachment. The good news: deploying SPF, DKIM, and DMARC authentication, enabling multi-factor authentication, training employees with phishing simulations, and using a secure email gateway are the foundational email security best practices that stop most attacks before they land.

Most businesses I speak with think they’re covered because they have antivirus and a spam filter. They’re not. Spam filters catch the obvious stuff. What gets through is the credible-looking phishing email that spoofs your CEO’s address, or the invoice that looks exactly like one from your real supplier. That’s what causes the real damage. This guide covers 12 email security best practices that address the full threat picture, from technical controls to the human element your technology can’t fix alone.

Why Email Is Your Biggest Security Liability

Email remains the primary delivery method for phishing attacks, business email compromise, malware, and ransomware, making it the most targeted communication channel in any organization.

The painful truth is that most email-based attacks don’t exploit software vulnerabilities. They exploit people. An attacker doesn’t need to break through your firewall if they can convince one of your staff to click a link, open an attachment, or wire funds to a fraudulent account. That’s a cheaper and far more reliable approach than technical hacking.

Business email compromise, or BEC, is a specific and particularly damaging attack. A criminal gains access to or impersonates a corporate email account, then uses it to authorize fraudulent wire transfers, redirect payroll, or manipulate supplier payments. BEC attacks don’t rely on malware. They rely on trust, and that’s what makes them so effective against organizations that haven’t implemented proper email security best practices.

Ransomware delivered via email attachments is the other major threat. A staff member opens what looks like a PDF invoice. Malicious code executes. Systems lock. The ransom demand arrives. Companies with no offline backups often have no choice but to pay. All of it starts with one email.

The threat isn’t theoretical. It’s happening to businesses your size, in your sector, right now. So treat your inbox like the front door it is, and start locking it properly.

Common Email Security Threats Every Business Faces

The email threat environment includes phishing, spear phishing, whaling, business email compromise, email spoofing, malware attachments, and ransomware, and each one requires a slightly different defensive response.

Most people know what phishing is in theory, but underestimate how targeted and convincing modern attacks have become.

Phishing, Spear Phishing, and Whaling

Standard phishing casts a wide net. Millions of emails go out impersonating banks, courier services, or government agencies, hoping a small percentage of recipients click. Your spam filter catches most of it.

Spear phishing is different. The attacker researches your business, your team, your suppliers, and your processes. The phishing email they send references real names, real projects, and real relationships. It looks legitimate because it’s designed specifically for your organization. Spam filters often let spear phishing through, because nothing about it looks generic.

Whaling targets senior executives. The CEO, the CFO, the managing director. These individuals have the authority to approve large transactions, and attackers know it. A well-crafted whaling email spoofing a board member can move hundreds of thousands of dollars before anyone questions it.

Business Email Compromise and Email Spoofing

Email spoofing is the technique behind most BEC attacks. An attacker forges the “From” field in an email so it appears to come from a trusted sender, whether that’s your CEO, your accountant, or a supplier. Without proper email authentication in place, your mail server has no way to verify the sender is who they claim to be.

BEC attacks enabled by email spoofing are among the costliest forms of cybercrime. They require no malware, no technical exploit, and no direct access to your systems. Just a convincing email and a trusting recipient.

Malware, Ransomware, and Malicious Attachments

Malware delivered through email attachments takes many forms: Word documents with malicious macros, weaponized PDFs, compressed archives hiding executables. Ransomware delivered via email is particularly damaging because the payload can spread across a network within minutes of a single click.

The defining characteristic of these attacks is that your employee is the entry point. No amount of network security stops ransomware once it’s running inside your perimeter with legitimate user credentials. That’s why email security best practices must combine technical controls with trained, alert people.

Email Authentication Protocols: SPF, DKIM, and DMARC Explained

SPF, DKIM, and DMARC are email authentication protocols that verify whether a sending mail server is authorized to send email on behalf of your domain, and together they form the technical backbone of any serious anti-spoofing strategy.

If you don’t have all three configured, anyone in the world can send email that appears to come from your domain. Your clients, your staff, your suppliers, all potential targets for an attacker impersonating you.

SPF: Sender Policy Framework

SPF is a DNS record that lists which mail servers are authorized to send email on behalf of your domain. When a receiving mail server gets an email claiming to be from your domain, it checks your SPF record. If the sending server isn’t on the list, SPF fails.

SPF alone isn’t enough. It only checks the envelope sender, not the visible “From” address your recipient actually sees. But it’s a necessary first layer, and without it, DMARC can’t function properly.

DKIM: DomainKeys Identified Mail

DKIM adds a cryptographic signature to outgoing emails. The receiving server uses a public key published in your DNS to verify the signature. If the email was tampered with in transit, the DKIM signature fails.

DKIM confirms two things: the email genuinely came from your domain, and the content wasn’t altered after it was sent. That second point matters for compliance purposes as much as security.

DMARC: The Policy That Ties It Together

DMARC (Domain-based Message Authentication, Reporting and Conformance) builds on SPF and DKIM. It tells receiving mail servers what to do when an email fails authentication checks: deliver it, quarantine it, or reject it outright.

DMARC also provides reporting. You get visibility into who is sending email using your domain, including attackers attempting to spoof your address. That intelligence is genuinely useful.

Setting DMARC to a “reject” policy is the goal. It means any email that fails SPF or DKIM gets blocked before it reaches your client’s or partner’s inbox. No more successful email spoofing from your domain. But move to “reject” carefully: start with a “none” policy to monitor, then move to “quarantine,” then “reject” once you’re confident legitimate mail is authenticating correctly.

SPF, DKIM, and DMARC together are not optional if you take email security seriously. They’re table stakes.

12 Email Security Best Practices for Your Business

The following email security best practices address both technical controls and the human behaviors that attackers exploit most reliably. Implement them in layers, because no single measure stops everything.

1. Enable Multi-Factor Authentication on Every Email Account

Multi-factor authentication (MFA) requires a second form of verification beyond a password, such as a one-time code sent to a mobile device or generated by an authenticator app, before granting access to an email account.

Stolen passwords are one of the most common routes into corporate email. Credential phishing, password reuse from breached sites, and brute-force attacks all produce usable passwords. MFA means a stolen password alone doesn’t get an attacker in. They’d also need the second factor, which they almost certainly don’t have.

Enable MFA on every email account in your organization, not just senior executives. Attackers target accounts with access to financial systems and sensitive data, which often includes accounts further down the hierarchy than you’d expect. Use an authenticator app rather than SMS where possible, because SMS-based MFA can be bypassed through SIM-swapping attacks.

If your team uses Microsoft 365 or Google Workspace, MFA is available and straightforward to enforce through the admin console. There’s no excuse not to have it switched on today.

2. Deploy SPF, DKIM, and DMARC Authentication

Deploying SPF, DKIM, and DMARC across your domain closes the email spoofing gap that attackers rely on to impersonate your business in phishing and BEC attacks.

Start by checking what’s currently configured. Tools like MXToolbox let you look up your existing SPF, DKIM, and DMARC records in seconds. Many businesses discover they have a partial setup, an SPF record but no DMARC policy, or a DMARC policy still set to “none” that provides reporting but no protection.

Work with your IT team or email provider to get all three correctly configured. Set DMARC reporting emails to an address someone actually monitors. Review the reports regularly. They’ll show you who’s attempting to send email using your domain, and that information will occasionally surprise you.

3. Use a Secure Email Gateway

A secure email gateway (SEG) filters all inbound and outbound email traffic before it reaches your mail server, scanning for phishing links, malware attachments, spam, and policy violations.

Your built-in spam filter isn’t a secure email gateway. A proper SEG uses multiple detection methods: reputation-based filtering, sandboxing to detonate suspicious attachments in a safe environment, URL rewriting to check links at the time of click, and machine learning to identify phishing patterns that signature-based tools miss.

Leading secure email gateway options include Proofpoint, Mimecast, and Cisco Secure Email. Microsoft 365 users can evaluate Microsoft Defender for Office 365, which provides SEG-like capabilities within the platform.

A secure email gateway is particularly valuable for blocking ransomware delivered via email attachments and catching the spear phishing attacks that generic filters miss. It’s one of the highest-return investments in your email security stack.

4. Run Security Awareness Training and Phishing Simulations

Security awareness training that includes regular phishing simulations is the most effective way to reduce the likelihood of your employees falling for phishing attacks, spear phishing attempts, and BEC schemes.

Technology stops a lot. But it doesn’t stop everything, and what gets through needs a trained human to catch it. Security awareness training teaches your people to recognize the warning signs of phishing emails: unexpected urgency, mismatched sender addresses, requests to bypass normal processes, suspicious links or attachments.

The training has to be ongoing. A one-hour session at onboarding that’s never repeated doesn’t change behavior. Monthly or quarterly phishing simulations, where you send realistic-looking fake phishing emails to staff and track who clicks, are far more effective. Employees who click receive immediate feedback and targeted training. Over time, click rates drop and reporting rates rise.

Platforms like KnowBe4 and Proofpoint Security Awareness Training make running phishing simulations and tracking results straightforward, even for small teams. The goal isn’t to shame staff who click. The goal is to build instincts through repetition.

Train your people. It’s the one control that gets better the more you invest in it.

5. Enforce a Strong Email Security Policy

A written email security policy sets the rules for how your organization creates, sends, handles, and retains email, and gives your team clear guidance on what to do when something looks suspicious.

Most SMEs don’t have a formal email security policy. They have unwritten norms, which is not the same thing. When someone gets a suspicious email, what do they do? Without a policy, the answer varies wildly across your team.

Your email security policy should cover acceptable use, password requirements, rules for handling sensitive information over email, attachment and link handling procedures, and a clear reporting process for suspected phishing. It should also specify what happens when the policy is violated.

Keep it readable. A 40-page document no one opens doesn’t protect you. A clear, well-communicated one-pager that staff actually understand does.

6. Implement Email Encryption for Sensitive Communications

Email encryption protects the content of messages in transit and at rest, preventing unauthorized parties from reading sensitive information even if they intercept the email.

Standard email is not encrypted by default. A message traveling between mail servers can be intercepted and read. For routine internal communication, the risk is often acceptable. For emails containing personal data, financial information, legal documents, or health records, it’s not.

Transport Layer Security (TLS) encrypts email in transit between mail servers. Most modern email platforms support TLS, but you should verify that your configuration enforces it rather than merely allows it. For end-to-end encryption where only the sender and recipient can read the content, S/MIME (Secure/Multipurpose Internet Mail Extensions) or PGP (Pretty Good Privacy) are the main options.

Email encryption is a compliance requirement in many sectors. If your business handles personal data under GDPR, health information under HIPAA, or financial data under relevant financial regulations, you need to know what your encryption posture is and whether it meets the standard. If you’re not sure, that’s the first thing to find out.

7. Activate Data Loss Prevention Controls

Data loss prevention (DLP) tools monitor outbound email for sensitive content, such as financial account numbers, personal data, or confidential documents, and either block or flag emails that violate your data handling policies.

DLP addresses a risk that pure inbound filtering doesn’t touch: data leaving your organization through email. This can happen maliciously, an insider threat exfiltrating client data, or accidentally, a staff member forwarding a file containing sensitive personal data to a personal address.

Microsoft 365 and Google Workspace both include DLP capabilities. You can configure policies that scan outbound emails for patterns matching credit card numbers, national insurance numbers, or other sensitive data formats, and route those emails for review or block them entirely. Purpose-built DLP tools offer more granular control for organizations with complex data handling requirements.

DLP isn’t just about security. It’s about regulatory compliance. A data breach caused by an accidental email with unprotected personal data can carry significant regulatory consequences. DLP is a practical control that reduces both the risk and your exposure.

8. Enforce Strong Password Policies and Prevent Account Takeover

Account takeover prevention starts with strong, unique passwords for every email account combined with multi-factor authentication, because compromised credentials are the most common path to unauthorized email access.

Weak or reused passwords remain a widespread problem. Your staff member who uses the same password for their email account and a compromised shopping site has handed attackers a direct route into your inbox. Credential stuffing attacks, where criminals use leaked username-password pairs to try access to corporate accounts, are automated and run continuously.

Password managers eliminate the excuse for weak or reused passwords. Tools like 1Password or Bitwarden generate and store strong, unique passwords for every account. Enforce minimum password length and complexity requirements through your identity provider or email platform admin settings.

Also review your offboarding process. Former employees whose email accounts remain active are an account takeover risk with no security awareness training and no reason to protect your interests. Disable accounts on the day of departure, not whenever IT gets around to it.

9. Control Email Attachment and Link Handling

Controlling how your organization handles email attachments and links, through technical restrictions, sandboxing, and clear employee guidance, significantly reduces the malware and ransomware risk from email.

Attackers use email attachments to deliver ransomware and other malware because it works. Your secure email gateway should sandbox suspicious attachments before they reach the recipient’s inbox, detonating them in an isolated environment to check for malicious behavior. Configure your email platform to block high-risk file types entirely, including executable files, macro-enabled Office documents, and compressed archives from unknown senders.

URL rewriting, available in most secure email gateways, rewrites links in inbound emails so they’re checked for malicious content at the time of click rather than at delivery. This catches phishing links that were safe when the email arrived but became malicious shortly after. It’s a simple but effective control against one of the most common phishing techniques.

10. Monitor Email Activity and Audit Regularly

Ongoing email monitoring and regular audits give you the visibility to detect account takeover, data exfiltration, policy violations, and email spoofing attempts before they cause serious damage.

You can’t protect what you can’t see. Email monitoring tools track anomalies: a user account suddenly sending hundreds of emails, login attempts from unusual locations, large file attachments going to external addresses. These patterns often indicate a compromised account or an insider threat in progress.

Set up alerts for high-risk behaviors in your email platform’s admin console. In Microsoft 365, the Microsoft Purview compliance portal provides audit logging and alerting. Regular reviews of your DMARC reports also fall into this category. Monitoring is only valuable if someone is actually looking at the output.

11. Have a Clear Incident Response Process for Email Threats

A documented incident response process for email security threats tells your team exactly what to do when a phishing email gets through, a BEC attack is detected, or an account is compromised, reducing the time between detection and containment.

Speed matters enormously when an account is compromised. Every minute a threat actor has access to a corporate email account, they’re reading messages, forwarding sensitive data, and potentially using the account to launch internal phishing attacks against your colleagues or clients. A clear process means no one wastes time deciding who handles it.

Your incident response plan for email threats should include: who to notify internally, how to isolate a compromised account, how to preserve evidence for investigation, when to involve external support, and how to communicate with affected clients or partners. Test it. An untested plan is a theoretical plan, and theoretical plans don’t hold up under pressure.

12. Manage Third-Party Email Risk and Vendor Access

Third-party and vendor email risk, including supplier impersonation in phishing attacks and BEC schemes, requires explicit controls beyond your internal email security posture.

Some of the most convincing phishing attacks impersonate your suppliers, law firms, or accountants. The attacker researches your business relationships and sends a fraudulent email that references a real project or ongoing engagement. Your team trusts the sender because they recognize the name. Standard email security controls may not flag it.

Establish clear out-of-band verification procedures for any email requesting a change in payment details, banking information, or access credentials. That means picking up the phone and calling a known contact number, not replying to the suspicious email or calling a number provided within it. This is the single most effective control against supplier impersonation BEC attacks, and it costs nothing to implement.

Also review what email access you’ve granted to third-party applications and services. SaaS tools that connect to corporate email accounts via OAuth can represent a significant attack surface if those tools are compromised or their access isn’t regularly reviewed. Audit and revoke access that’s no longer needed.

Building an Email Security Culture, Not Just a Security Stack

Technical email security controls are necessary, but the organizations that hold up best under attack are the ones where security awareness training has built a culture of suspicion and reporting, not just compliance.

The technology is the easy part. Once SPF, DKIM, and DMARC are configured, your secure email gateway is deployed, and MFA is enforced, your technical posture is substantially improved. But phishing simulations only produce lasting behavior change if the culture around them is right.

Make it safe to report suspicious emails. If someone reports a phishing simulation and gets ridiculed for being cautious, they’ll stop reporting real threats. Build a reporting culture where flagging a suspicious email is the expected, rewarded behavior, not an embarrassing admission. Your IT team should make it easy: a single button in the email client, a Slack channel, whatever reduces the friction.

Revisit your security awareness training program at least quarterly. Phishing techniques evolve. The spear phishing emails circulating now are more convincing than the ones from two years ago, partly because attackers now have access to tools that help them craft highly personalized lures at scale. Your training needs to reflect current attack patterns, not outdated examples that your staff can spot immediately.

You can read more about building a broader security culture and managing human risk in our cybersecurity guide for SMEs. It covers the organizational and behavioral dimensions that technology alone can’t address.

Compliance, DMARC Reporting, and Email Governance

Email security best practices and regulatory compliance are closely linked, and your DMARC reporting, email encryption posture, and DLP controls often determine whether you meet your obligations under GDPR, HIPAA, or sector-specific regulations.

GDPR requires appropriate technical measures to protect personal data. If personal data is transmitted via unencrypted email or your domain can be spoofed to send fraudulent emails to data subjects, those are arguable compliance failures. DMARC at “reject” policy, enforced TLS for email in transit, and DLP controls over outbound email all contribute directly to GDPR compliance.

HIPAA-covered entities in the US must ensure that protected health information transmitted via email is encrypted. S/MIME or PGP encryption for emails containing health data isn’t optional for covered entities; it’s a regulatory requirement.

Keep records of your email security posture: your DMARC configuration and reports, your security awareness training completion rates, your phishing simulation results, your DLP policy logs. In the event of a regulatory investigation or a cyber insurance claim following a breach, that documentation demonstrates that you took reasonable and proportionate steps to protect your systems and data. Boards and senior leadership should be reviewing email security metrics, not just IT teams.

For a broader look at how email security fits into your overall compliance and risk management approach, our data protection and compliance resources are a useful next step.

Frequently Asked Questions About Email Security Best Practices

What is the single most important email security best practice?

If you had to pick one, enable multi-factor authentication on every email account. A stolen password is the most common route into corporate email, and MFA stops credential-based attacks even when passwords are compromised. After MFA, deploying DMARC at “reject” policy is the next highest-impact step.

What is the difference between SPF, DKIM, and DMARC?

SPF specifies which mail servers can send email on behalf of your domain. DKIM adds a cryptographic signature to outgoing emails to verify authenticity and detect tampering. DMARC defines the policy for what happens when emails fail SPF or DKIM checks, and provides reporting on authentication results. All three work together, and you need all three for effective email authentication.

How do phishing simulations improve email security?

Phishing simulations send realistic fake phishing emails to your staff and measure how many click, how many provide credentials, and how many report the email. The results identify who needs additional training and what attack types your team is most vulnerable to. Run them regularly, not as a one-off exercise, and use the data to target your security awareness training program.

What is business email compromise and how do you prevent it?

Business email compromise (BEC) involves an attacker impersonating a trusted person, often via email spoofing or account takeover, to fraudulently authorize payments, redirect funds, or extract sensitive information. Prevention requires DMARC authentication to block spoofed emails, MFA to prevent account takeover, and out-of-band verification procedures for any email requesting financial transactions or changes to payment details.

Do small businesses need a secure email gateway?

Yes. Small businesses are frequently targeted precisely because attackers assume their defenses are weaker. A secure email gateway blocks the phishing attacks, malware attachments, and ransomware delivery attempts that bypass basic spam filters. Cloud-based secure email gateway options are available at price points accessible to SMEs, and the cost is a fraction of the cost of a successful ransomware attack or BEC fraud.

How does email encryption protect my business?

Email encryption protects message content from being read by unauthorized parties during transmission or if stored emails are accessed. TLS encrypts email in transit between mail servers. S/MIME provides end-to-end encryption so only the intended recipient can decrypt and read the message. For businesses handling personal data, financial information, or legally privileged communications, email encryption is both a security measure and a compliance requirement.

What should an email security policy include?

An email security policy should cover: acceptable use of corporate email, password and MFA requirements, rules for handling sensitive data via email, procedures for attachments and external links, the process for reporting suspected phishing, and consequences for policy violations. It should be written in plain language, communicated to all staff, and reviewed at least annually.

Start with What Matters Most

Email security is not a single product you buy and forget about. It’s a layered approach: technical controls like SPF, DKIM, DMARC, MFA, a secure email gateway, email encryption, and DLP, working alongside trained, alert people who know what phishing looks like and what to do when they see it.

If you’re not sure where your organization stands, start there. Audit your current DMARC configuration. Check whether MFA is enforced on every email account. Ask your IT team when phishing simulations were last run and what the results showed.

You don’t need to do everything at once. But you do need to start. The businesses that get hit hardest by BEC fraud, ransomware, and phishing attacks are almost always the ones that knew they should do something and kept delaying.

Pick the two or three email security best practices from this list that your organization hasn’t implemented yet, and get them done this month. Then come back for the next ones. If you want to understand how email security fits into your broader risk and resilience picture, our cyber risk assessment guide walks through the full process.

Secure your systems. Train your people. Don’t wait for a breach to tell you what was missing.