A single convincing email can send a staff member to a fake Microsoft 365 sign-in page, redirect a supplier payment, or expose customer information. That is why knowing how to secure business email is less about buying one security product and more about putting sensible layers around the way your team already works.
For most small and medium businesses, email is the front door to payroll, cloud files, customer records and financial systems. It deserves the same care as your premises keys or online banking. The good news is that the strongest improvements are practical, affordable and manageable without turning every email into a chore.
Start with the accounts that matter most
Email security begins with identity. If an attacker gets into a staff member’s mailbox, they can read sensitive correspondence, reset passwords for other systems and impersonate that person internally or with customers.
Every business email account should have a unique, long password managed through a reputable password manager. Reusing passwords across email, supplier portals and personal services is risky. A breach at one unrelated service can give criminals a password they will immediately try against Microsoft 365, Google Workspace and banking portals.
Multi-factor authentication, often called MFA, should be enabled for every account. This adds a second check, such as an authenticator app approval or security key, before a person can sign in. It is one of the most effective ways to prevent account takeover when a password is stolen.
Not all MFA methods offer the same protection. Authenticator apps and security keys are generally stronger than text message codes, which can be vulnerable to SIM-swap fraud. For businesses handling payments, confidential client information or privileged access, consider phishing-resistant sign-in methods such as passkeys or hardware security keys.
Access also needs to reflect each person’s role. A casual staff member does not need administrator rights, and a former employee should not retain access to a shared mailbox or cloud drive. Review users, licences, mailbox permissions and admin roles whenever someone joins, changes roles or leaves.
How to secure business email against phishing
Phishing emails have become more polished. They may copy a supplier’s branding, refer to a real project, or appear to come from a director asking for something urgently. The goal is usually to steal sign-in details, install malicious software or change payment information.
Technical filtering helps, but it will not catch everything. Staff need a simple decision-making habit: pause when an email creates urgency, asks for a password, requests a payment change or directs them to a sign-in page.
Teach your team to check the sender’s full email address, not only the display name. A message that says it is from a manager may actually come from a similar-looking external address. They should hover over links before opening them, avoid unexpected attachments, and contact the sender through a known phone number or a new email message if a request seems unusual.
Payment changes deserve a separate process. Do not rely on an emailed bank account update alone, even if it appears to come from a regular supplier. Confirm it by calling a verified contact number. This small control prevents a common and costly form of business email compromise.
Short, regular awareness sessions work better than one annual training session staff forget by February. Use real examples relevant to your business, explain what to look for, and make reporting easy. People are far more likely to report a suspicious message when they know they will be thanked rather than blamed.
Secure your email domain as well as inboxes
Your email domain, such as yourbusiness.com.au or yourbusiness.co.nz, should be protected from spoofing. Without the right settings, criminals can send messages that look as though they came from your business, damaging customer trust and increasing the chance that someone pays a fraudulent invoice.
Three domain settings matter here: SPF, DKIM and DMARC. They sound technical, but their purpose is straightforward. SPF identifies which services may send email for your domain. DKIM adds a digital signature to messages. DMARC tells receiving email systems how to handle messages that fail those checks and provides reporting on attempted abuse.
Setting these up takes care because many businesses send email through more than one platform. For example, you may use Microsoft 365 for day-to-day correspondence, a CRM for campaigns, an accounting system for invoices and a website form service for notifications. If a legitimate sender is missed, its emails may fail delivery.
A sensible approach is to identify every approved sending service, configure SPF and DKIM correctly, then begin DMARC in monitoring mode. Once the reports show that legitimate email is passing reliably, move towards a stricter policy. This is an area where managed IT support can save time and prevent accidental disruption.
Keep devices and email apps under control
A well-protected mailbox can still be exposed through an unprotected laptop or mobile. Devices that access business email should have screen locks, current operating system updates, supported security software and encrypted storage. Lost or stolen devices are less damaging when the information on them cannot be easily accessed.
For staff using personal mobiles, the right balance depends on the business. Requiring a device PIN and allowing business data to be removed remotely may be enough for a small team. Businesses with more sensitive information may need mobile device management to separate work data from personal apps and enforce security settings.
Also review which email apps and third-party services have access to mailboxes. Staff sometimes approve a calendar tool, PDF service or AI assistant without realising it can read messages or contacts. Remove old integrations and only approve services with a clear business purpose.
Back up what email security cannot prevent
Email platforms retain data well, but retention is not always the same as a recoverable backup. A user can delete a folder, a retention policy can expire, or a ransomware incident can affect connected files and data. A separate backup strategy provides a more reliable recovery option.
Decide what needs protecting: mailboxes, calendars, contacts, OneDrive or SharePoint files, and shared mailboxes often used for customer service or accounts. Make sure backups are monitored, retained for an appropriate period and tested. A backup that has never been restored is an assumption, not a recovery plan.
Your incident plan should also be clear enough for a busy team to follow. If someone enters their password into a suspicious website, they should report it immediately. The response may include resetting the password, revoking active sessions, checking mailbox rules, reviewing sign-in activity and notifying affected customers or suppliers where necessary.
Speed matters. Attackers often create hidden forwarding rules or send fraudulent messages from a compromised mailbox within minutes. Having a trusted IT contact and clear escalation path reduces the time between discovery and containment.
Make security part of normal operations
The best email security is not a one-off project. New staff arrive, software changes, suppliers are added and criminals adjust their tactics. Review your settings and access at least quarterly, and reassess after major changes such as an Office 365 migration, merger, new finance system or staff restructure.
For a sole trader, the priority may be MFA, a password manager, phishing awareness and a secure backup. For a larger organisation, conditional access policies, managed devices, email threat protection and formal incident response processes may be justified. The right level of protection depends on the information you hold, the financial risk you carry and how much disruption your business can tolerate.
The Computer Professors can help businesses turn these controls into a practical managed security plan, without burying staff in jargon or unnecessary restrictions. Good email security should let your people get on with their work confidently, while making it much harder for the wrong person to get in.