Secure Email for Business: Email Encryption Best Practices

Email is a cornerstone of business communication. Without it, many companies would grind to a near-halt. Unfortunately, email is also a leading cause of data breaches and business interruptions.

Why is business email encryption so crucial, and how can secure email safeguard businesses and their customer data?

Although inbound attacks such as phishing are on the rise, the most common risk to businesses comes from the messages they send out into the world.

Outbound email risks include:

• Email interception, where confidential information is intercepted by an unauthorised third party on its way to the intended recipients.
• Email misfires, where an unsecured confidential email is misaddressed and delivered to unauthorised third parties due to human error.

Outbound email risks are the most common causes of business email compromise, leading to reputation damage and regulatory fines.

So, how can a business protect itself from sending unsecured confidential information?

Let's explore how secure email for businesses can help you avoid outbound email risk.

What Is Secure Email?

Secure email is a comprehensive term for encryption and authentication solutions designed to protect outbound emails from falling into the wrong hands.

Secure email solutions for businesses provide two primary layers of protection:

• Email encryption disguises email contents and attachments so they can’t be accessed if intercepted.
• Email authentication locks emails behind an authentication challenge that recipients must correctly answer to open them.

Although all email providers offer some level of encryption and authentication, these are usually designed for everyday consumer emails.

For businesses handling sensitive customer information, the features provided by their email provider might not meet certain standards of compatibility, ease of use, and regulatory compliance.

Let’s examine your options for business email encryption and authentication when using Outlook, Gmail, and Apple Mail.

We’ll break down the pros, cons, and alternative solutions.

How to Secure Business Emails Using Microsoft 365/Outlook

Microsoft 365 and Outlook are part of an expansive ecosystem, so your secure email options differ depending on your business package.

Let’s take a look.

Microsoft Purview Message Encryption (Basic)

Availability: Eligible Microsoft 365 and Office 365 plans; availability depends on licence, tenant configuration, and whether Azure Rights Management is active.

Microsoft Purview Message Encryption can encrypt business emails both within and outside your organisation and the Microsoft ecosystem.

Microsoft says Purview encrypted email can be read directly in supported Outlook clients, including new Outlook, Outlook on the web, Outlook for iOS and Android, Outlook for Windows 2019 and newer, and Microsoft 365.

Recipients using other mail services receive instructions for opening the protected message.

That account-based access can reduce some risk, especially where account-level MFA and rights management policies are in place.

However, it is not the same as asking each recipient to pass a message-specific Q&A, SMS, or sector identity check before opening sensitive customer information.

Pros:

• Messages are auto-decrypted for recipients using Outlook.

Cons:

• No Mailock-style message-level Q&A, SMS, or sector identity challenge for the recipient.
• Only supports authentication for Microsoft attachments (e.g., docx, xls).
• Revocation is not the same as Outlook recall and depends on Advanced Message Encryption conditions.
• Recipients outside supported Outlook experiences may need to open the protected message through Microsoft's web flow.

Initialisation:

• User option in Outlook: To encrypt an email in Outlook, click the “Encrypt” button above the compose pane and select “Encrypt” (You may need to add this option to your toolbar by selecting “Customise Toolbar” first.)
• Administrator message rules: Microsoft says admins can configure mail flow rules in the Exchange Admin Centre or Exchange Online PowerShell, provided Microsoft Purview Message Encryption is available and configured in the tenant.

Microsoft Purview Message Encryption (Advanced)

Availability: Eligible plans and add-ons; check Microsoft licensing and tenant configuration before relying on specific advanced controls.

Microsoft Purview Message Encryption (Advanced) brings additional controls and features to Microsoft Purview Message Encryption, including branding, expiry, and conditional revocation for eligible link-based encrypted emails.

Options to revoke and set expiry periods on secure emails provide a last-resort lockdown option for your business emails.

Keyword triggers are useful for initiating security based on your company’s policies regarding personal data and information security.

These can be set up so that an email will be encrypted if particular phrases are detected.

However, advanced controls still depend on how the message is encrypted and opened. Microsoft says messages delivered through the native inline experience in supported Outlook clients cannot be revoked through Advanced Message Encryption.

If a recipient's mailbox or account is compromised, firms should consider whether account-level controls are enough for the sensitivity of the information being sent.

Initialisation:

• User option in Outlook, where available for the user's client, licence, and organisation settings.
• Administrator message rules, using Microsoft Purview Message Encryption mail flow rules.
• Email keyword triggers: To configure advanced mail flow encryption rules using keywords and other information formats, see this guide.

Pros:

• Messages are auto-decrypted for recipients using Outlook.
• Branded templates for an improved recipient experience.

Cons:

• No Mailock-style message-level Q&A, SMS, or sector identity challenge for the recipient.
• Only supports Microsoft attachments (e.g., docx, xls).
• Revocation is conditional and depends on recipients receiving a link-based, branded encrypted email rather than a native inline Outlook experience.

How to Secure Business Emails Using Gmail and Apple Mail

Gmail and Apple Mail offer no secure email functionality that can support a business in encrypting emails at scale without compatibility issues.

TLS and S/MIME are offered but neither guarantees delivery and security to all recipients when used alone.

There is also no authentication capability within Gmail or Apple Mail to make sure that recipients must verify their identity to gain access.

Emails sent using their encryption are no more secure than the rest of the emails in a recipient’s inbox.

Few information security regulators would advise using Gmail or Apple Mail’s native capabilities (regardless of updates) to secure sensitive information and comply with regulatory guidance.

For this reason, let’s explore how third-party secure email can help.

Secure Email for Gmail and Apple Mail

If you’re using Gmail or Apple Mail for your business, don’t worry - you can still send confidential information securely by email.

You have two options to secure your communications:

Secure Webmail

Many secure email solutions (such as Mailock Pro) provide a web browser-based interface, allowing you to log in to compose secure emails, add attachments, and set authentication challenges for recipients.

Secure Email Gateways

Some secure email solutions (such as Mailock Enterprise) offer an encryption gateway, which can be hosted on-premise or in the cloud.

Confidential emails pass through it to be secured before they leave your infrastructure.

Gateway encryption can be initiated using keywords, rules, or API calls triggered by custom functionality within your email infrastructure.

The solution you use will depend on the scale of your operation and the volume of confidential information being shared.

Why Is Multi-Factor Authentication So Important?

“Secure” email covers more than blocking hackers, scammers, and other bad actors.

It also means preventing the release of sensitive information - like customer names, credit card numbers, and addresses.

Encrypting an email protects data on its way to an inbox, but it doesn’t ensure it gets to the right person.

That distinction matters when firms send pension, mortgage, or identity documents by email and need to know who can open them.

Here are the most important reasons why multi-factor authentication should be a key part of securing your sensitive business emails:

• Multi-factor authentication offers message-level security so that, even if someone gains access to one of your recipient’s email inboxes, they cannot open an email containing confidential information or files.
• Multi-factor authentication provides evidence that information has been delivered to the right person - in professional services, this is often a requirement for regulatory compliance in certain transactions.
• Multi-factor authentication prevents 99.9% of automated cyber-attacks according to a study conducted by Microsoft.
• Multi-factor authentication prevents the most common cause of a data breach - human error - if a sensitive email is sent to the wrong address, they are unable to open it without passing a challenge.

Protect Your Business

Outbound email risk is now a routine concern for firms handling customer data.

Misaddressed messages, intercepted attachments, and inbox compromise all create regulatory and reputational exposure.

Encryption and multi-factor authentication reduce that exposure when they fit how your teams actually send sensitive information.

Whether you use Outlook, Gmail, or Apple Mail, the right setup depends on volume, client expectations, and compliance requirements.

Getting those controls in place protects client data and supports the evidence regulators and customers expect.

FAQs

What Is the Difference Between Email Encryption and Authentication?

Email encryption protects the content of an email during transmission, ensuring it cannot be read if intercepted.

Authentication verifies the recipient’s identity, adding a layer of security to ensure the email reaches the intended person.

Why Should Businesses Avoid Relying on Native Email Security Features?

Native features like TLS and S/MIME provide basic encryption but lack universal compatibility and multi-factor authentication, making them insufficient for securing sensitive business communications.

How Does Multi-Factor Authentication Improve Email Security?

Multi-factor authentication requires an additional step beyond a password, such as a code or biometric verification, ensuring that only the intended recipient can access sensitive emails.

Are Gmail and Apple Mail Suitable for Secure Business Communication?

Gmail and Apple Mail lack built-in encryption and authentication features, making them unsuitable for handling confidential business information without third-party tools.

What Are the Benefits of Using Third-Party Secure Email Solutions?

Third-party solutions can add advanced encryption, recipient authentication, and features such as message revocation, helping firms tailor controls to business needs.

References

Check Your Email Security and Protect Your Customers, National Cyber Security Centre, 2024

Set Up New Message Encryption Capabilities, Microsoft, 2024

Define Mail Flow Rules to Encrypt Email, Microsoft, 2022

Message Encryption FAQ, Microsoft Learn, 2026

Revoke Email Encrypted by Advanced Message Encryption, Microsoft Learn, 2026

Send S/MIME or Microsoft Purview Encrypted Emails in Outlook, Microsoft Support, 2026

One Simple Action You Can Take to Prevent 99.9% of Account Attacks, Microsoft, 2019

Human Error Is Responsible for 85% of Data Breaches, GRCeLearning, 2022

Reviewed by

Sam Kendall, 02.06.26

This content is for general information only and is not legal advice.