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10 Email Server Security Best Practices to Secure Your Email Server

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(Email Server Security) If your business relies heavily on email for customer communication, safeguarding your email server is imperative. Here are some pivotal email server security practices to fortify your organization’s digital fortifications.

Consider this scenario: you’re bracing for an imminent hurricane (a situation all too familiar for Floridians). You reinforce your roof with straps, secure all outdoor items by moving them into your garage or shed, board up your windows and doors, and stockpile food and water for potential power outages.

However, if you neglect to close your home’s exterior doors as the storm approaches, you might as well bid farewell to your house and its contents. Similarly, failing to secure your email server is akin to leaving those doors wide open.

According to Radicati, the daily volume of business and consumer emails is projected to exceed 376 billion by 2025. If you send emails without a secure server or Email Server Security, your data your business’s lifeblood is vulnerable to interception and misuse. Safeguarding your sensitive information is non-negotiable.

But what constitutes a secure email server? Let’s delve into 10 crucial email server security best practices and underscore the necessity of these measures to shield your business and clientele.

Let’s unravel this further.

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Defining a Secure Email Server Security

As the term “secure or (Email Server Security) ” suggests, a secure email server protects your email domain and its data from unauthorized access. This encompasses:

  • Safeguarding emails during transmission and while stored in employees’ inboxes.
  • Blocking unauthorized users from dispatching emails using your organization’s domain.
  • Configuring email filters and antivirus measures on your servers.
  • Securing the networks your employees and authorized users employ to access email services.
  • Safeguarding the tangibility of electronic mail servers from unapproved entities, particularly when administrating one’s own server infrastructure.
  • Understanding the security measures your business email service provider (such as Amazon WorkMail, Google Workspace, Rackspace, Microsoft Exchange, etc.) undertakes to protect the servers hosting your organization’s email data.

But how can these Email Server Security measures be implemented? Let’s delve into the essentials…

10 Essential Email Server Security Practices to Implement Now

The following list of email server security practices provides an excellent starting point to enhance your email server’s security.

1. Modify All Default Settings, Usernames, and Passwords for Your Email Server

A common oversight by organizations is neglecting to change default server settings and configurations, often due to time constraints or unawareness of the risks involved. Always take the time to adjust these settings.

This encompasses modifying standard login credentials. Safeguarding accounts and passwords is paramount in the realm of cybersecurity. Using default usernames and weak passwords is akin to opting for a fragile chain lock on your front door instead of a robust double deadbolt. Although it offers minimal security, an intruder can easily breach it with minimal effort.

Employing default credentials for your server or software is similarly insecure and exposes your email server and its data to theft and other threats.

2. Implement Mail Transfer Agent Strict Transport Security (MTA-STS)

MTA-STS is a protocol that enforces strict transport security for incoming emails (Email Server Security). As per Google, “SMTP liaisons for email procure heightened security when the dispatching server endorses MTA-STS, and the recipient server imposes an MTA-STS mandate.”

In simpler terms, enabling MTA-STS on your organization’s email server ensures that emails are only received via secure, authenticated connections (using TLS 1.2 or 1.3).

This protocol protects recipients from unauthenticated messages sent through insecure connections, preventing potential malware insertion or data modification during transmission, commonly known as a man-in-the-middle (MitM) attack.

If the sender’s digital identity cannot be authenticated or SSL/TLS is not enabled, the message will be rejected.

A basic illustration showing how enabling MTA-STS on your domain helps secure your email server and message recipients by automatically rejecting messages sent via insecure connections from unauthenticated users.

Email Server Security
Email Server Security

3. Select Secure Email Protocols to Safeguard Your Communications in Transit

Establishing a secure MTA is merely a fragment of the comprehensive strategy; additional measures are imperative to fortify your server and the communications it handles, both incoming and outgoing.

Install an SSL/TLS Certificate on Your Server to Facilitate HTTPS

Are you aware that SSL/TLS extends to email as well (Secure Email Servers)? Indeed, you can harness SSL/TLS security to safeguard the communication conduit of your messages. This enables the encryption of interactions between your email server and other email servers, thereby preventing interception during transit.

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Each time an employee dispatches or receives an email, a connection with the recipient’s email server is established. An unsecured connection allows knowledgeable adversaries to intercept and potentially alter the message, unbeknownst to the involved parties.

Furthermore, if an email signing certificate is utilized to directly encrypt email data (which will be elaborated upon later), it adds an extra layer of security to your communications.

Utilize Secure Ports for Your Inbound and Outbound Email Services

Typically, IMAP or POP3 protocols manage incoming emails (i.e., messages retrieved by email clients from your mail server), while SMTP governs outgoing emails. Ensure the configuration of your services to the following secure TCP/IP ports for incoming and outgoing messages:

  • Outbound: Secure port 465 or 587 (with STARTTLS enabled) for SMTPS
  • Inbound: With SSL/TTLS enabled, utilize the following ports:
    • Port 993 for IMAP (with SSL enabled)
    • Port 995 for POP3 (with SSL enabled)

4. Embrace DMARC to Prevent Brand Domain Spoofing

Cybercriminals revel in masquerading as reputable companies to exploit their reputations. Impersonation of organizations is a common tactic in phishing schemes. According to Check Point, the most impersonated brand in Q1 2022 was LinkedIn, implicated in over half (52%) of the phishing attacks analyzed globally. In Q4 2021, DHL held this undesirable title, with Microsoft as the previous leader.

Domain-based message authentication, reporting, and conformance (DMARC) is an email protocol designed to shield your domain from unauthorized usage. The Internet Engineering Task Force (IETF) introduced it to aid organizations in defending their domains against fraudulent activities. (Email Server Security) DMARC builds upon two other authentication protocols to ensure only authorized users send emails on behalf of your domain:

  • Sender Policy Framework (SPF): An SPF text record is attached to your domain name system (DNS), validating messages sent by your domain.
  • DomainKeys Identified Mail (DKIM): This protocol affixes your digital signature to outbound email headers, leveraging public key cryptography to authenticate and ensure the integrity of emails from your domain.

How prevalent is DMARC? Mimecast’s “The State of Email Security 2022” report reveals that nearly 90% of companies are either utilizing DMARC or planning to within the next year. This statistic is based on a global survey of 1,400 IT and cybersecurity professionals across 12 countries.

To elevate your organization’s digital identity further, consider integrating Brand Indicators for Message Identification (BIMI) and Verified Mark Certificates (VMCs). This integration enables the insertion of your verified logo into all outbound emails from legitimate senders, enhancing brand authenticity and trust.

5. Maintain Server Software and Firmware Through Regular Updates and Patches

Operating your server with outdated or unpatched software is akin to inviting catastrophe. Patches serve as the developers’ method to rectify bugs and mitigate issues that render your email servers susceptible to threats. Failing to implement these patches promptly exposes you to the risk of cyber adversaries exploiting these weaknesses to infiltrate your email servers and access sensitive data.

A crucial decision you’ll face is the mode of implementing these updates. Will you manage them manually or explore automated solutions? Both approaches come with their own advantages and drawbacks, but the essential point is to ensure updates and patches are diligently applied, preventing scenarios akin to the Eternal Blue incident.

(Brief overview): Eternal Blue was a vulnerability in older Windows systems for which Microsoft released a patch. However, many organizations delayed applying this patch, leading to a ransomware attack that compromised hundreds of thousands of devices worldwide, affecting millions of individuals.)

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6. Implement Email Server Firewalls for Monitoring Traffic

We are now past the halfway mark in our discussion of best practices for securing email servers. Similar to network firewalls, email server firewalls filter inbound and outbound traffic based on predefined rules. This mechanism allows you to monitor communications entering and exiting your domain, helping to identify and address any suspicious activities.

An illustration of how an email server firewall helps to block suspicious traffic.

Email Server Security
Email Server Security

Of course, we can’t give you any specific directions about setting up rules on your email server since every system is different. So, you’ll need to refer to your specific firewall manufacturer’s site for specifics on how to accomplish this goal.

Set Rate Limits and Size Restrictions on Outbound Traffic

While it’s important to monitor your traffic, you’ll also want to be sure to restrict both the number of emails that can originate from your domain as well as their sizes. A spike in outbound messages could indicate that one or more of your authorized accounts could be compromised and is being used to send spam or phishing messages. Setting rate limits can help protect your domain’s reputation.

7. Exercise Discretion in Allocating Mail Server Access

It cannot be overstressed that access to critical systems must be judiciously granted. This principle applies universally, from sensitive customer and employee databases to the sanctity of your email servers. Implementing stringent access management protocols is essential.

Employee profiles should be configured to provide only the necessary access levels required for job functions. Should an individual need access to a protected system for a specific project, grant temporary permissions, ensuring these privileges are rescinded once the task is concluded.

Moreover, establish a robust procedure to ensure the prompt revocation of access rights upon an employee’s departure. Both malicious actors and discontented former staff may exploit dormant credentials to infiltrate systems. Preempt this risk by immediately deactivating such accounts.

8. Embrace Passwordless SSH Authentication for Server Administration

As an administrator, the secure shell (SSH) protocol is indispensable for managing servers. Traditionally, this involves a username-password combination for authentication. However, a more secure alternative exists: public-private key pairs.

This cryptographic method authenticates users through a pair of keys one public, one private confirming your identity as an authorized user. This approach facilitates secure, password-free authentication, mitigating the risks associated with weak credentials.

We’ve previously delved into SSH key management best practices. To summarize, effective SSH key management is pivotal in safeguarding your cryptographic keys as part of your overall security strategy. For a comprehensive overview, refer to our detailed article on this subject.

9. Educate Users on Account Email Server Security Practices

Safeguarding account credentials is non-negotiable; it is the duty of each employee and network user. Why? Because compromised user accounts are the most straightforward vector for hackers to breach your server. Strengthening your organization’s cyber defenses involves comprehensive user education and training on cybersecurity best practices.

Effective cybersecurity (Email Server Security) awareness training should encompass:

  • Identifying and avoiding social engineering and phishing threats (utilizing real-world examples)
  • Protocols for handling suspicious emails or phone calls (specific guidance and contact points)
  • Strategies for creating secure passwords (with enforcement measures)
  • Utilizing single sign-on (SSO) and password management tools
  • Avoiding the installation of unauthorized software (shadow IT)

10. Mandate Digital Signatures and Email Encryption for Authorized Users

To safeguard against credential phishing, enforce the use of digital signatures for all email communications, particularly for administrators and privileged users. A cryptographic digital signature, verified by a public certificate authority (CA), offers dual assurances:

  1. Verifies the sender’s legitimacy (Email Server Security).
  2. Ensures the integrity of the email content.

Additionally, use these certificates to encrypt sensitive email data. Both sender and recipient must possess email signing certificates, with the sender using the recipient’s public key for encryption. The recipient then decrypts the email with their private key.

If this process seems daunting, simply request a digitally signed email from the recipient initially. This provides you with their public key, simplifying future encrypted communications.

Final Reflections on the Imperative of Secure Email Servers

Implementing these email server security practices is paramount for organizations globally. Chiefly, email encryption is imperative to uphold the trust placed in you by customers, users, and stakeholders.

Furthermore, securing your email server safeguards your data from cybercriminals and competitors who covet your digital assets.

Consider these additional reasons for prioritizing email server security:

  • Protects data from unauthorized access
  • Prevents data breaches and compromises
  • Averts brand and reputational damage from security incidents
  • Ensures compliance with data privacy and security regulations (GDPR, CCPA, PCI DSS, etc.)
  • Mitigates the direct and indirect costs associated with an insecure email server (including breach mitigation, legal actions, and noncompliance penalties)