Email Security Best Practices Every Business Should Follow

Why Email Security Matters More Than Ever

Email is still the number-one attack vector for cybercriminals. According to the FBI’s Internet Crime Complaint Center, business email compromise alone cost organizations over $2.9 billion in 2023. And it’s not just large enterprises getting hit — small and mid-sized businesses are increasingly targeted because attackers know their defenses are often thinner.

The good news: most email-based attacks are preventable. With the right combination of technical controls, employee training, and policy enforcement, you can dramatically reduce your exposure. Here’s what every business should have in place.

Start with Email Authentication: SPF, DKIM, and DMARC

If you haven’t configured SPF, DKIM, and DMARC for your domain, you’re leaving the front door wide open. These three protocols work together to verify that emails claiming to come from your domain actually come from your domain.

SPF (Sender Policy Framework)

SPF tells receiving mail servers which IP addresses are authorized to send email on behalf of your domain. It’s a DNS record that lists your legitimate sending sources — your mail server, your marketing platform, your CRM, and so on. When an email arrives claiming to be from your domain but comes from an unlisted IP, the receiving server knows something is off.

Setting up SPF is straightforward, but it requires an accurate inventory of every service that sends email using your domain. Miss one, and legitimate emails start bouncing. Include too many, and you weaken the protection. This is where working with an experienced email security provider pays off.

DKIM (DomainKeys Identified Mail)

DKIM adds a digital signature to your outgoing emails. The receiving server checks this signature against a public key published in your DNS records. If the signature matches, the server knows the email hasn’t been tampered with in transit and genuinely originated from your domain.

Think of DKIM as a tamper-evident seal on every message you send. Without it, attackers can intercept and modify emails mid-delivery — changing invoice details, swapping out links, or altering instructions.

DMARC (Domain-based Message Authentication, Reporting, and Conformance)

DMARC ties SPF and DKIM together and tells receiving servers what to do when an email fails both checks. You can set it to monitor only (p=none), quarantine suspicious messages (p=quarantine), or reject them outright (p=reject).

Most organizations should start with monitoring mode to see what’s happening, then gradually move toward reject. DMARC also sends you reports showing who’s trying to send email as your domain — which is often eye-opening.

Together, these three protocols stop domain spoofing, reduce phishing that impersonates your brand, and improve your email deliverability. If you’re not sure where your domain stands, a quick DNS check will tell you.

Email Filtering and Threat Detection

Authentication protocols protect your outbound reputation. But you also need strong inbound filtering to catch threats before they reach your employees’ inboxes.

Spam and Malware Filtering

Modern email filters go well beyond simple spam detection. They scan attachments for malware, check URLs against known threat databases, and use machine learning to identify suspicious patterns. If you’re still relying on the default filtering that comes with your email platform, you’re likely missing threats that a dedicated security layer would catch.

Advanced Threat Protection

More sophisticated attacks — like zero-day malware or carefully crafted spear-phishing emails — require advanced threat protection (ATP). ATP solutions sandbox suspicious attachments, meaning they open and test files in an isolated environment before delivering them. They also rewrite URLs so that links are checked at the moment of click, not just at the moment of delivery.

This matters because attackers increasingly use time-delayed tactics: they send a clean link that redirects to a malicious site hours after delivery, long after the initial scan.

Outbound Filtering

Don’t overlook outbound filtering. If an employee’s account is compromised, outbound filters can detect unusual sending patterns — mass emails, messages with suspicious attachments, or communications with known bad domains — and block them before damage spreads.

Email Encryption: Protecting Data in Transit and at Rest

Email was never designed to be secure. By default, messages travel across the internet in plain text, readable by anyone who intercepts them. For businesses that handle sensitive data — financial records, health information, legal documents, customer PII — encryption isn’t optional.

Transport Layer Security (TLS)

TLS encrypts the connection between mail servers, protecting emails in transit. Most major email providers support TLS, but it’s opportunistic by default — meaning if the receiving server doesn’t support it, the email goes through unencrypted anyway. You can enforce TLS for specific domains (like your bank or legal counsel) to guarantee encryption on those communications.

End-to-End Encryption

For truly sensitive communications, end-to-end encryption ensures that only the sender and intended recipient can read the message. Solutions like Microsoft 365 Message Encryption or S/MIME make this practical for business use without requiring recipients to install special software.

The key is making encryption easy enough that employees actually use it. If the process is cumbersome, people find workarounds — and workarounds usually mean less security, not more.

Phishing Awareness Training

Technology catches a lot, but it can’t catch everything. The most effective phishing emails are the ones that look completely legitimate — because they’re modeled on real business communications. Your employees are your last line of defense, and they need to be prepared.

What Good Training Looks Like

Effective phishing training isn’t a once-a-year compliance checkbox. It’s ongoing, practical, and based on real-world examples. Good programs include:

• Simulated phishing campaigns that test employees with realistic fake attacks, then provide immediate feedback when someone clicks
• Role-specific training — your finance team faces different threats than your marketing team
• Short, frequent modules rather than hour-long annual sessions that everyone forgets
• Clear reporting procedures so employees know exactly what to do when they spot something suspicious

Building a Reporting Culture

The goal isn’t to shame people who click on phishing links. It’s to build a culture where reporting suspicious emails is encouraged and easy. If employees are afraid of getting in trouble, they won’t report — and an unreported phishing email that someone clicked is far more dangerous than one that’s flagged immediately.

Make the reporting process simple: a one-click button in the email client that sends suspicious messages to your IT or security team for analysis.

Attachment and Link Policies

Not every file type belongs in an inbox. Establishing clear policies about what can and can’t be sent via email reduces your attack surface significantly.

File Type Restrictions

Block executable file types (.exe, .bat, .cmd, .ps1, .js) at the email gateway. There’s rarely a legitimate business reason to email these files, and they’re a favorite delivery method for malware. For file types that are commonly weaponized but sometimes legitimate — like macro-enabled Office documents (.docm, .xlsm) — consider quarantining them for manual review rather than blocking outright.

Safe File Sharing Alternatives

For large files or sensitive documents, encourage the use of secure file-sharing platforms instead of email attachments. Services like SharePoint, OneDrive, or other managed file-sharing tools provide better access controls, audit trails, and malware scanning than email ever will.

Link Protection

Implement URL rewriting so that every link in incoming emails passes through a security check when clicked. Train employees to hover over links before clicking and to be suspicious of shortened URLs or links that don’t match the expected domain.

Mobile Email Security

Your employees are reading and responding to email on their phones — probably more than on their desktops. Mobile email security deserves its own attention.

Mobile Device Management (MDM)

MDM solutions let you enforce security policies on devices that access company email. This includes requiring passcodes, enabling remote wipe capabilities, enforcing encryption, and separating work data from personal data. If an employee loses their phone, you need to be able to remove company email and data from that device immediately.

Approved Email Apps

Not all email apps are created equal. Some third-party email apps store credentials insecurely or sync data to uncontrolled cloud services. Require employees to use approved email applications that meet your security standards — typically Outlook or your platform’s native app.

Public Wi-Fi Risks

Employees checking email at coffee shops, airports, and hotels are connecting through networks they don’t control. Require VPN use for accessing company email on public networks, or better yet, ensure your email platform enforces encrypted connections regardless of the network.

Account Security and Access Controls

Even the best email filters won’t help if an attacker gets legitimate access to an employee’s account. Strong account security is foundational.

Multi-Factor Authentication (MFA)

MFA should be mandatory for every email account in your organization — no exceptions. Even if an attacker steals a password through phishing, credential stuffing, or a data breach, MFA stops them from actually logging in. Use app-based authenticators or hardware keys rather than SMS codes, which are vulnerable to SIM-swapping attacks.

Password Policies

Require strong, unique passwords for email accounts. Better yet, implement a password manager so employees don’t reuse passwords across services. The most common way email accounts get compromised isn’t through sophisticated hacking — it’s through password reuse. An employee uses the same password for their email and a random website, that website gets breached, and suddenly their email account is exposed.

Conditional Access

Conditional access policies let you control email access based on context — device compliance, location, risk level, and more. For example, you can block email access from unmanaged devices, require MFA when logging in from a new location, or restrict access to certain countries where your business doesn’t operate.

Email Retention and Data Loss Prevention

Email security isn’t just about keeping bad things out. It’s also about keeping sensitive data from leaking out — whether through malicious intent or honest mistakes.

Data Loss Prevention (DLP) Rules

DLP policies scan outgoing emails for sensitive content — credit card numbers, Social Security numbers, health records, proprietary data — and either block the email, require encryption, or notify an administrator. These rules catch accidental data exposure, like an employee emailing a spreadsheet of customer data to the wrong person.

Retention Policies

Define how long email should be retained and when it should be deleted. This matters for compliance (many regulations specify retention periods) and for reducing risk (old emails are a liability in litigation). Automated retention policies ensure consistency without relying on individual employees to manage their own mailboxes.

Incident Response: When Something Gets Through

No security setup is perfect. You need a plan for when a phishing email gets clicked, an account gets compromised, or sensitive data gets sent to the wrong place.

Your email incident response plan should include:

• Immediate containment — disabling compromised accounts, revoking active sessions, resetting credentials
• Investigation — determining what was accessed, what was sent, and who was affected
• Notification — informing affected parties and, if required, regulatory bodies
• Remediation — closing the gap that allowed the incident and updating controls
• Documentation — recording what happened and what was done, for both compliance and future prevention

Having this plan written down and rehearsed before an incident happens makes the difference between a contained event and a full-blown crisis.

Putting It All Together

Email security isn’t a single product or a one-time project. It’s a combination of technical controls, user education, and ongoing management that evolves as threats change. The businesses that get this right treat email security as a continuous program, not a set-it-and-forget-it task.

If you’re not sure where your email security stands today, that’s a reasonable place to start. An assessment of your current setup — authentication records, filtering rules, access controls, and policies — will show you exactly where the gaps are and what to prioritize.

BrightWorks IT helps businesses build and maintain email security programs that actually work. Whether you need to implement DMARC, deploy advanced threat protection, or train your team to spot phishing, we can help you get there without the complexity.

Ready to strengthen your email security? Request a free assessment and we’ll review your current setup and recommend practical next steps.