IT manager testing outbound email security using laptop
14 min

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 vs outbound secure email gateways

 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 recall and auditing capabilities to ensure emails are delivered to their intended recipients.

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. 1/4 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 recipients' email addresses to each other, 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.

Misdirected emails are a leading example of human error in cybersecurity, contributing to 95% of security breaches


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 the use of 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 6 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, and this is especially the case for regulated industries such as financial services.

The primary data protection regulation that businesses must adhere to is GDPR, which is enforced by the Information Commissioner's Office (ICO).

Under GDPR, companies have an obligation to take accountability for the data under their care and ensure the privacy of personal information.

Organisations that send sensitive information by unsecured email open themselves to outbound risks, and if a data breach occurs, are law-bound to report the incident to the ICO within 72 hours.

report an email breach to the ICO

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.

Such a policy should define the types of information that are considered sensitive, outline what is considered the 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 potential security gaps and adapt to a changing threat landscape.

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

Necessary changes will include updating security software, patching vulnerabilities, and revising policies as a result.

3. Introduce Employee Education And Awareness Training

Employee awareness is critical for building a strong security culture and increasing the success of an outbound email security strategy.

Regular training should be conducted to educate staff on the importance of data security, enabling them to adhere to company email policies and utilise email in a manner that does not place sensitive data at risk.

Awareness training can involve anything from interactive workshops to simulations. It should help employees to understand the consequences of a data breach and the critical preventative role they play.

4. Integrate An Outbound Email Security Solution

Awareness of outbound email risks, on its own, is not enough.

Organisations should implement a dedicated secure email solution to assist employees in preventing outbound email data leaks.

The right solution can enable the protection of sensitive data against interception and manipulation, as well as human error.

Over 361.6 billion emails are sent and received daily worldwide

Key Features Of Outbound Email Security Solutions

Outbound email security solutions employ a variety of techniques to ensure data is protected on its journey.

 Email Encryption

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

It transforms your email messages and attachments into a coded format that is indecipherable to human eyes.

This process is achieved through the use of cryptographic 'keys' which encode and decode the email content.

When end-to-end encryption methods, such as AES-256, are employed, these ciphers are practically impossible to crack.

However, the basic TLS encryption methods provided by many email service providers fall short when it comes to sensitive emails.

The difference is important for businesses to understand:

Transport Layer Security (TLS) — This type of encryption is the one most commonly used by email providers.

TLS encrypts the connection between the sender and the recipient, securing messages during their transit between email servers.

However, TLS encryption has limitations:

  • Emails are only encrypted during transmission, leaving them unprotected when stored on a server or in an inbox.
  • For TLS encryption to work effectively, both the sender and recipient must use TLS-compatible email services.

End-to-End Encryption — This is a more robust form of encryption used by outbound email security solutions.

With end-to-end encryption, emails are encrypted directly on the sender's device before being sent and remain encrypted until they are decrypted by the intended recipient.

Digital documents can be timestamped and encrypted for compliance with regulatory standards

End-to-end encryption offers several advantages:

  • It secures emails at all stages, both in transit and at rest.
  • Only the sender and recipient have access to the decryption keys, significantly reducing the risk of third-party interception.

For businesses transmitting sensitive information via email, the strength of the encryption algorithm used is also important.

 Encryption Algorithms

Data Encryption Standard (DES) — DES was one of the earliest digital encryption algorithms and has since become outdated in its original form due to vulnerabilities. To enhance its security, an evolved version known as Triple DES (3DES) is often used.

This method involves the application of three distinct 56-bit DES keys in succession, creating an effective key length of 168 bits.

Despite this improvement, the relatively short key length in modern standards means that Triple DES is not as secure as newer algorithms and can be slow due to its triple encryption process.

Rivest-Shamir-Adleman (RSA) — RSA is a form of asymmetric encryption, which means it uses two different keys; a public key for encryption and a private key for decryption.

This separation of keys enhances security, as the private key does not need to be shared or transmitted, reducing the risk of interception.

RSA's mathematical operations make it considerably slower than other methods, so it is often used in digital signatures rather than for encrypting large amounts of data directly.

Advanced Encryption Standard (AES) — AES is a symmetric encryption algorithm, meaning the same key is used for encryption and decryption.

It is used by the military for its robust security, and offers key sizes of 128, 192, and 256 bits, providing strong resistance against various attacks.

AES's primary advantage is its speed and efficiency in processing large amounts of data, making it a preferred choice for many applications, including for email encryption.


While encryption is a powerful tool to prevent interception, it doesn't address the issue of human error.

An additional layer of authentication can verify a recipient's identity before they gain access to a message.

This means that even if an email is sent to the wrong inbox, it remains inaccessible to unauthorised individuals.

There are multiple authentication methods available to secure outbound email communications:

Single-Factor Authentication (SFA) — This basic form of authentication typically requires just a username and password for access, such as your regular email account login details.

Passwords can be vulnerable to brute force attacks, compromised through access to devices that remain logged in, or simply guessed if they are predictable enough.

In the context of sensitive data, relying solely on password-based authentication is insufficient.

31% of businesses have 2FA

Multi-Factor Authentication (MFA or 2FA) — MFA adds an extra layer of security by requiring users to pass an identity challenge, making it significantly harder for unauthorised individuals to breach.

MFA can combine three types of authentication factors:

  • Something you have:
    • For instance, entering a code sent via SMS to a mobile phone.
  • Something you know:
    • Such as responding to a security question.
  • Something you are:
    • Involving biometrics, like fingerprint or facial recognition.

Adding multi-factor authentication to emails ensures that:

  1. Any emails that are sent to the wrong person can’t be opened.
  2. If someone gains unauthorised access to a recipient’s inbox, they can’t read the sensitive message within it.

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

 Data Loss Prevention (DLP)

Data Loss Prevention (DLP) is an essential component of outbound email security solutions, and is designed to safeguard sensitive information from being inadvertently or maliciously shared outside an organisation.

This technology plays a crucial role in preventing data breaches and ensuring compliance with regulatory standards.

DLP systems work by scanning and analysing outgoing email content and attachments for sensitive data.

This process is governed by a set of predefined rules and policies that are tailored to an organisation's specific data protection requirements.

For example, a DLP policy might be configured to detect and block the transmission of personally identifiable information (PII), financial details, confidential business plans, or other sensitive data.

The core functionalities of DLP in outbound email security include:

Content Inspection and Contextual Analysis — DLP tools can inspect the content of emails for sensitive information, employing deep content analysis and contextual understanding.

This might involve scanning for specific keywords, patterns (like credit card numbers), or even unstructured data types such as images and video.

Advanced DLP understand the context in which information is shared, differentiating between safe and potentially harmful transmissions.

Deploying email security is vital to reduce business and management risk.

Policy Enforcement and Compliance — DLP systems can enforce corporate data handling policies and ensure that data being shared is compliant with regulatory standards such as GDPR.

Such policies are often customised to align with a specific regulatory environment and organisational risk profile.

User Behaviour Monitoring and Risk Management — By monitoring email traffic, DLP solutions cam help to identify unusual patterns or behaviours that indicate a risk of data leakage or non-compliance.

They can provide insights into user activity, helping to refine data protection strategies and mitigate potential data loss incidents.

Incident Management and Remediation — In the event of a policy violations, DLP tools can provide alerts and detailed reports, allowing for immediate investigation and response.

Some solutions offer remediation options, such as blocking outbound data transmission or quarantining emails.


Maintaining audit trails for digital communications is no longer just a best practice – it’s a regulatory necessity.

Audit trails serve as comprehensive records of electronic communications, logging various details about emails sent and received.

This detailed record-keeping is not just vital for regulatory compliance, it can also aid with business intelligence and analysis.

When considering a secure outbound email solution, there are key elements of an email that should be logged:

Sender and Recipient Details — Tracking who sent an email and who received it, including any CC’ed or BCC’ed recipients, is essential.

Timestamps — Recording the date and time when an email was sent and when it was opened provides a chronological context to communication.

Content and Attachments — It's crucial to maintain detailed records of an email's content and any attachments. This includes the nature of the attachments and any sensitive information they may contain.

Access and Interaction — Monitoring who accessed an email, including forwards, replies, or interactions, such as clicking on links, is important.

Metadata — Capturing metadata like email headers, IP addresses, and server logs offers deeper insights into an email's journey and security.

Changes and Version Control — For emails that are part of ongoing threads or conversations, it's important to keep a record of changes and different versions of these communications.

Outbound email security solutions often offer compliance or audit dashboards that offer detailed analysis of email data.

 Email Revoke

Sometimes confused with email recall, revoke is the ability to retract an email after it has been sent, remotely blocking recipient access.

It differs from email recall in that recall is most often associated with the ability to request that your recipient deletes a message.

Email revoke is particularly valuable in scenarios where sensitive information was accidentally sent to the wrong person.

Many email clients, such as Outlook and Gmail, offer email revocation, but with limitations

Revoke effectively 'retrieves' the email from the recipient's inbox, mitigating the risk of data falling into the wrong hands and isolating potential security breaches before they worsen.

Email providers such as Microsoft Outlook offer in-built recall functions. However, these often have significant limitations that prevent them from being used to secure sensitive business or customer data.

Outbound email solutions offer unilateral revoke functions that are able to completely block access to email messages that have been sent.

Choosing An Outbound Email Security Solution

When evaluating and choosing the right solution for your business, there are a number of other factors you may want to consider.

 Business Size

The most appropriate outbound email security solution will vary depending on the size of your business.

Small to medium-sized enterprises (SMEs) might prefer cost-effective, easy-to-manage solutions, whereas larger enterprises might require more comprehensive, customisable solutions.

For example, our secure email solution Mailock can be offered on a singular license basis for small firms, all the way up to a cloud or on-premise hosted secure email gateway for large organisations.


Choosing a solution that can grow with your business is important.

If you plan to securely communicate with large numbers of customers in the future, your solutions should be able to handle these volumes.

It is also important that the outbound email security solution you use can evolve as your business meets larger and changing threats.


Any successfully integrated security solution balances security with user convenience.

The outbound email security system you choose shouldn’t be so complex that it hinders everyday operations, causes friction in customer comms or requiring extensive training.

Look for intuitive interfaces and user-friendly features that simplify the management of outbound emails.


Consider both upfront costs and long-term expenses.

This includes subscription fees, maintenance costs, and any additional charges for updates or support.

Evaluate the cost against the features provided to ensure it offers value for money and won't require unforeseen additional investment.


Reliable customer support is vital for ensuring the smooth operation of an outbound email solution.

Choosing a provider that offers comprehensive support across a range of channels to assist with troubleshooting, training, and assistance with updates is key.


The solution should seamlessly integrate with your existing IT infrastructure, including existing email software and networks.

Consider how the solution will interact with other security tools and software already in use to ensure that friction is kept to a minimum.


Research the provider's reputation in the market.

Take the time to read customer reviews and case studies to get the full picture of the provider's track record in terms of reliability, innovation, and responsiveness to new threats.

Securing Your Business Email: The Imperative of Outbound Email Security

As email continues to be a vital communication tool in both business and personal spheres, understanding and implementing robust outbound email security measures is no longer optional but a necessity.

ML FS Boost portal usage

With increasing email users and the corresponding rise in threats, businesses must proactively safeguard their outbound communications.

This entails not just protecting sensitive information but also maintaining a strong reputation, ensuring regulatory compliance, and ultimately preserving the trust of clients and stakeholders.

By adopting comprehensive outbound email security solutions that encompass encryption, multi-factor authentication, DLP, and meticulous auditing, organisations can effectively mitigate the risks of human error and data interception, thereby securing the integrity of their electronic communications in this ever-evolving digital landscape.

If you're looking for comprehensive outbound email security for your business' communications, consider Mailock secure email.

Deliver sensitive information securely with Mailock


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, 12.06.24


Originally posted on 07 12 23
Last updated on July 5, 2024

Posted by: Sabrina McClune

Sabrina McClune, an expert researcher with an MA in Digital Marketing, was a finalist in the Women In Tech Awards 2022. She excels in conducting and compiling research for B2B tech companies. Sabrina enjoys reading fantasy novels and collecting special edition books.

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