What Is Outbound Email Security? Protecting Sensitive Data

Email remains a key communication tool for both business and personal use. According to studies, the number of email users worldwide continues to grow, with an estimated 4.37 billion users in 2023, and a predicted 4.73 billion users by 2026.

Millions of businesses, from small enterprises to large corporations, rely on email for internal and external communication, marketing, customer relations, and more.

There's just one problem - email is at risk from a range of digital threats.

And while awareness of inbound attacks is rising, many companies underestimate the threat that emails leaving their organisation pose.

That’s where outbound email security comes in.

Understanding Email Security: Inbound Vs. Outbound

Inbound and outbound email security are two sides of the same coin.

Both are essential for a robust cybersecurity strategy that safeguards information and enables reliable email communications.

Inbound Email Security

Inbound email security encompasses the measures and technologies needed to protect an organisation from incoming email threats.

These include malicious emails that enter a business’s network such as spam, phishing, malware, viruses, and other harmful content.

Inbound email security solutions typically involve spam filters, antivirus scanning, phishing detection, and other techniques to identify and block dangerous emails before they reach a recipient's inbox.

Outbound Email Security

Outbound email security encompasses the measures and technologies that monitor and manage emails sent out from an organisation.

The main objective of outbound email security is to prevent the leakage of sensitive information and comply with data protection regulations.

Outbound email security solutions offer technologies such as encryption, authentication, data loss prevention (DLP), email revoke, and auditing to ensure emails are delivered to their intended recipients securely.

What Are Outbound Email Threats?

When considering the primary threats to data transmitted via email, the two main risks are human error and interception.

Human Error

Human error in email use is one of the main causes of a data breach. Key examples of human error in action include:

Misdirected Emails - Sensitive information sent to the wrong recipient is the most common email error. A quarter of UK adults have accidentally shared personal data via email with the wrong recipient.

Incorrect Use of BCC and CC Fields - Mistakenly putting recipients in the 'Cc' (Carbon Copy) field instead of 'Bcc' (Blind Carbon Copy) can expose email addresses, breaching confidentiality.

Accidental Attachment of Sensitive Files - Attaching the wrong file, especially one containing sensitive data like personal or financial information, can lead to unintended exposure.

Interception

Interception involves unauthorised access to emails at various stages in their journey. Attacks can involve:

Compromised Sending Devices - If a sender's device is infected with malware or otherwise compromised, emails can be intercepted or altered.

Compromised Recipient Devices - If a recipient's device is compromised, the confidentiality and integrity of incoming emails can be breached.

Network Interception - Emails transmitted over unsecured or public networks without encryption can be intercepted.

Email Server Breaches - If attackers gain access to email servers, they can intercept, read, or manipulate unsecured emails.

Why Do Businesses Need Outbound Email Security?

The importance of outbound email security cannot be understated.

Not only is protecting outbound emails essential for regulatory compliance, it is critical to business continuity.

Protect Data

32% of UK businesses and 24% of charities have experienced a data breach or attack, resulting in an estimated 2.39 million instances of cybercrime and 49,000 instances of fraud.

Data sent by unsecured email is the top cause of a data breach.

Implementing outbound email security can mitigate this risk, ensuring the confidentiality and integrity of sensitive data.

Maintain Reputation

Businesses that experience a data breach take a significant hit to their reputation. Research shows 81% of consumers would stop engaging with a brand if their data was involved in a leak.

It's estimated that 60% of small companies go out of business within six months of falling victim to a breach or cyber attack.

Organisations that implement outbound email security measures minimise the risk of a data incident, future-proofing their business.

Ensure Compliance

Organisations are held to high standards of data protection, especially in regulated industries like financial services.

The primary regulation is GDPR, enforced by the Information Commissioner's Office (ICO).

Under GDPR, companies must take accountability for the data they manage and protect personal information appropriately.

Sending sensitive information by unsecured email opens organisations to outbound risks. If a data breach occurs, they are legally obligated to report it to the ICO within 72 hours.

Best Practices for Implementing Outbound Email Security

Thinking about how best to tackle outbound email threats for your organisation? There are multiple elements to consider.

1. Develop a Comprehensive Security Policy

Creating a robust security policy is essential when implementing outbound email security measures for your organisation.

The policy should define the types of information considered sensitive, outline acceptable use of email, and specify procedures for handling outbound data.

2. Regularly Update and Audit Security Measures

Outbound email security is not a set-and-forget solution - regular audits and updates are necessary to identify and fix security gaps and adapt to a changing threat landscape.

Audits should be completed frequently and thoroughly, covering technical aspects and organisation-wide adherence to policies.

Updates may include patching vulnerabilities, upgrading software, and revising policies based on new threats.

3. Introduce Employee Education and Awareness Training

Employee awareness is critical to building a strong security culture and enhancing the success of your outbound email strategy.

Regular training should be provided to help staff understand the importance of data security, follow email usage policies, and avoid exposing sensitive data.

Training can include interactive workshops and simulated breaches. It should demonstrate the consequences of a data breach and highlight the preventative role employees play.

4. Integrate an Outbound Email Security Solution

Awareness alone is not enough. Organisations must implement a dedicated secure email solution to assist employees in preventing outbound data leaks.

The right solution protects sensitive data against interception and human error.

Key Features of Outbound Email Security Solutions

Outbound email security solutions employ a variety of techniques to protect data during its journey from sender to recipient.

Email Encryption

Encryption is a powerful tool that protects your email communications against interception and other malicious threats.

It transforms email messages and attachments into a coded format that cannot be read without a cryptographic key.

Using encryption methods like AES-256, emails are nearly impossible to decipher without authorised access.

However, the basic TLS encryption used by many providers often falls short when handling sensitive content.

Transport Layer Security (TLS) - TLS encrypts the connection between mail servers during transit. But:

• Emails are only encrypted during transmission, not when stored in inboxes or servers.
• Both sender and recipient must use TLS-compatible services for it to work effectively.

End-to-End Encryption - A more robust option that encrypts the email on the sender's device and keeps it encrypted until it reaches the intended recipient.

This ensures that only authorised parties with decryption keys can access the content, significantly reducing the risk of third-party interception.

For businesses sending sensitive information by email, the strength of the encryption algorithm is essential.

 Encryption Algorithms

Data Encryption Standard (DES) - DES was one of the earliest digital encryption algorithms. Triple DES (3DES) applies the DES cipher three times to each data block, strengthening its protection. However, 3DES is now outdated and slower than modern alternatives.

Rivest-Shamir-Adleman (RSA) - RSA is an asymmetric encryption method that uses a public key to encrypt and a private key to decrypt. This improves security, but the process is slow, so RSA is typically used for digital signatures rather than bulk data.

Advanced Encryption Standard (AES) - AES is a symmetric algorithm using 128, 192, or 256-bit keys. It's fast and secure, and widely used in commercial and government contexts, including secure email platforms.

Authentication

While encryption helps prevent interception, it doesn’t stop human error.

Authentication adds an extra layer by verifying the recipient’s identity before allowing access to a message.

This means if an email is sent to the wrong person, it remains inaccessible to unauthorised users.

Single-Factor Authentication (SFA) - Usually just a username and password. These are vulnerable to brute force attacks, guessing, or device compromise, so on their own, they aren’t secure enough for sensitive data.

Multi-Factor Authentication (MFA or 2FA) - MFA requires users to pass more than one identity check, making it harder for attackers to gain access.

It typically combines these factors:

• Something you have: e.g. a one-time SMS code
• Something you know: e.g. an answer to a security question
• Something you are: e.g. biometrics like fingerprint or facial recognition

Adding MFA to emails ensures that:

1. Any emails sent to the wrong recipient can’t be opened.
2. Even if someone gains access to a recipient’s inbox, they won’t be able to read the message.

Outbound email security solutions use multi-factor authentication to verify recipients before allowing messages to be decrypted.

Data Loss Prevention (DLP)

Data Loss Prevention (DLP) is critical to outbound email security. It prevents sensitive data from being inadvertently or maliciously shared outside your organisation.

DLP tools scan outgoing emails for specific data types and apply rules to block or flag potential breaches.

They are tailored to an organisation’s compliance requirements and risk profile, helping maintain data security across all communications.

Content Inspection and Contextual Analysis - DLP tools inspect the body and attachments of emails for sensitive information using keyword detection, pattern matching (e.g. credit card numbers), and context-aware analysis. They differentiate between safe and risky transmissions.

Policy Enforcement and Compliance - DLP systems enforce corporate policies and ensure outbound data meets legal and regulatory standards, such as GDPR.

User Behaviour Monitoring and Risk Management - Monitoring outbound email activity can flag unusual behaviours, such as sending large volumes of sensitive data. This helps mitigate threats and informs security strategies.

Incident Management and Remediation - If a violation occurs, DLP tools alert security teams, quarantine or block the email, and generate audit trails for analysis and compliance reporting.

Auditing

Maintaining audit trails for digital communications is not just best practice - it’s a regulatory requirement.

Audit logs track email interactions and security actions. This includes:

• Sender and Recipient Details - Who sent it, who received it.
• Timestamps - When it was sent, received, and opened.
• Content and Attachments - What was included and its sensitivity.
• Access and Interaction - Link clicks, replies, and forwards.
• Metadata - Email headers, IP addresses, and server info.
• Changes and Version Control - Tracking edits and threads.

Outbound email security solutions often include compliance dashboards that provide visibility and insights into email usage and risks.

Email Revoke

Sometimes confused with recall, revoke allows you to remotely block access to an email after it has been sent.

Recall typically requests deletion. Revoke forces it, even if the email has landed in the wrong inbox.

This is particularly valuable when sensitive data is accidentally shared with the wrong recipient.

Secure email solutions provide unilateral revoke features to fully retract a message and prevent access to its content.

Choosing an Outbound Email Security Solution

When evaluating outbound email tools, consider how well the solution aligns with your business needs, infrastructure, and risk profile.

Business Size

The right outbound email security solution will vary by business size.

SMEs often need cost-effective, easy-to-use solutions. Larger enterprises may require customisable, highly scalable tools.

For example, Mailock can scale from a single licence to a cloud-hosted or on-premise secure email gateway.

Scalability

Choose a solution that can grow with your business. If your communication volume increases, your security tool should handle it.

It should also be able to adapt to evolving threats and changes in your infrastructure.

Ease of Use

Security shouldn't slow your business down. A good outbound email tool balances security with usability.

Look for user-friendly features and intuitive interfaces that minimise training needs and avoid disrupting customer communications.

Cost

Evaluate both upfront and ongoing costs. This includes licences, maintenance, updates, and support.

Compare features vs. cost to determine value. Make sure you won’t face unexpected upgrade or integration charges.

Support

Reliable customer support is essential for operational continuity.

Look for providers that offer multi-channel support with onboarding, training, and troubleshooting assistance.

Integrations

Your solution should integrate seamlessly with your existing IT environment, including email platforms, CRM systems, and other security tools.

This reduces friction and ensures a smoother implementation process.

Reputation

Research the provider’s track record and customer feedback.

Explore case studies and reviews to ensure they have a proven reputation for reliability and innovation in security.

Securing Your Business Email: The Imperative of Outbound Email Security

Email is a vital communication tool - but without the right safeguards, it puts your business at risk.

With more email users and rising threats, businesses must proactively protect outbound messages to maintain compliance, trust, and operational resilience.

By implementing strong outbound email security - including encryption, authentication, DLP, auditing, and revoke capabilities - organisations can reduce the risks of human error and cyber threats.

Looking for secure outbound email for your business? Explore Mailock secure email.

References

Number of Email Users Worldwide, Oberlo, 2023

Cyber Security Breaches Survey 2023, UK Government, 2023

60% of Small Companies Close Within 6 Months of Being Hacked, Cybersecurity Ventures, 2024

Reviewed by

Sam Kendall, 12.06.24

Sabrina McClune, 19.06.25