What Is MTA-STS?

Why Every Business Needs
This Essential Email Security Standard

What is MTA-STS? An Overview

Email is the primary tool of modern business communication systems.

Unfortunately, E-Mail systems are also one of the most targeted by cyber criminals.

While many organizations have implemented protections such as spam filtering and multi-factor authentication, one critical layer of email security is often overlooked—Mail Transfer Agent Strict Transport Security (MTA-STS).

MTA-STS is an increasingly important email security standard that helps ensure your emails are delivered securely using encrypted connections. For businesses looking to strengthen their cybersecurity posture, improve customer trust, and reduce the risk of intercepted email communications, implementing MTA-STS is a smart investment.

Improve Email Security & Prevent Email Interception

Mail Transfer Agent Strict Transport Security (MTA-STS) is an email authentication and encryption standard that helps protect email messages while they are travelling between mail servers.

Normally, when one email server sends a message to another, it attempts to use Transport Layer Security (TLS) encryption. However, if encryption fails, many mail servers simply fall back to sending the message without encryption.

This creates an opportunity for attackers to intercept communications through downgrade attacks or man-in-the-middle attacks.

MTA-STS eliminates this weakness by allowing domain owners to publish a policy that tells sending mail servers:

Always use TLS encryption.
Verify the receiving mail server’s certificate.
Do not deliver email if a secure encrypted connection cannot be established.

The result is significantly stronger protection for email communications.

The Importance of MTA-STS

Cyber attacks are becoming increasingly sophisticated, and email remains one of the primary targets. Without enforced encryption, attackers may be able to:

Intercept confidential emails
Read sensitive customer information
Capture financial documents
Modify email content during transmission
Steal intellectual property
Conduct business email compromise (BEC) attacks

MTA-STS helps prevent these risks by ensuring email is transmitted securely from one server to another.

For organizations handling customer data, financial information, healthcare records, or legal documents, secure email delivery is no longer optional—it’s a business necessity.

The Business Benefits of MTA-STS

1. Protecting Sensitive Information

Every day organisations exchange confidential information such as:

Contracts
Payroll data
Financial Reports
Customer Records
Intellectual Property
Legal documentation

MTA-STS helps ensure this information remains encrypted whilst being transmitted across the Internet.

2. Reduce the Risk of Email Interception

Cybercriminals frequently attempt to intercept email traffic using network attacks.

Without MTA-STS, attackers may be able to force email servers to abandon encryption altogether.

MTA-STS prevents these downgrade attacks by enforcing encrypted delivery.

3. Improve Customer Confidence

Customers expect organizations to protect their personal information.

Implementing recognized email security standards demonstrates your organization takes cybersecurity seriously.

This can improve :

Customer Trust
Brand reputation
Partner confidence
Vendor relationships

4. Support Regulatory Compliance

Many regulations require organisations to protect confidential information during transmission.

Examples include:

Australian Privacy Act
GDPR
HIPAA
PCI DSS
ISO 27001 security frameworks

While MTA-STS alone does not ensure compliance, it supports secure communication practices expected by many regulatory frameworks.

5. Reduce Cyber Security Risk

A successful email compromise can cost an organization far more than the effort required to implement modern email security.

Potential consequences include:

Data breaches
Financial fraud
Regulatory fines
Loss of customer confidence
Business disruption

MTA-STS helps reduce these risks by strengthening one of the most frequently targeted communication channels.

MTA-STS vs TLS

Many people assume TLS alone provides end-to-end protection.

Bluntly – It Does Not!

TLS is capable of encrypting email traffic.

However, without MTA-STS there is no guarantee encryption will actually be enforced. If encryption cannot be negotiated, many mail servers simply send the message anyway.

MTA-STS changes this behavior by requiring encrypted delivery.

Think of TLS as the lock. MTA-STS ensures the lock is actually used and locked-on

Should Every Business

Implement MTA-STS?

If your organization sends or receives email, the answer is almost certainly yes. Businesses of every size benefit from stronger email security.

This includes:

Professional services
Healthcare providers
Financial services
Manufacturing
Retail
Education
Government
Technology companies
Managed Service Providers (MSPs)
Not-for-profit organizations

Even small businesses are increasingly targeted by cyber criminals because they often have fewer security controls

MTA-STS Vs DMARC - DKIM and SPF

One of the most common misconceptions is that MTA-STS replaces SPF, DKIM or DMARC.

Each technology solves a different problem.

Technology	Purpose
SPF	Verifies authorised sending mail servers
DMARC	Prevents spoofing and phishing using SPF and DKIM alignment
DKIM	Confirms message integrity using digital signatures
MTA-STS	Protects email while it travels between mail servers
TLS-RPT	Reports failed encrypted email deliveries

Together these technologies create a layered email security strategy.

Best Practices for Implementing MTA-STS

When deploying MTA-STS, organisations should also:

Enable TLS Reporting (TLS-RPT)
Implement SPF
Configure DKIM correctly
Enforce DMARC policies
Use valid SSL certificates
Monitor email delivery reports
Regularly review DNS records
Test email security after configuration changes

Email security should be treated as an ongoing process rather than a one-time project.

MTA-STS - Frequently Asked Questions

Does Microsoft 365 support MTA-STS?

Yes. Microsoft 365 supports MTA-STS, although organisations are responsible for publishing the required DNS records and policy files for their domains.

Does Google Workspace support MTA-STS?

Yes. Google Workspace also supports MTA-STS and recommends its use alongside other email authentication technologies

Is MTA-STS difficult to implement?

For organizations with modern email infrastructure, implementation is generally straightforward. An experienced IT provider or Managed Service Provider can usually deploy and validate MTA-STS with minimal disruption.

Does MTA-STS stop phishing?

No.
MTA-STS protects email during transport. To combat phishing, organisations should also implement SPF, DKIM, DMARC, user awareness training, and advanced email filtering.

Does MTA-STS encrypt email?

MTA-STS does not perform encryption itself. Instead, it enforces the use of TLS encryption and prevents email from being delivered over insecure connections

MTA-STS

Why Businesses Should Act Now

Cyber threats continue to evolve, and attackers are constantly looking for weaknesses in business communication systems. While many organizations focus on endpoint protection and identity security, securing the transport of email is just as important.

MTA-STS provides an additional layer of defense by ensuring email is delivered over authenticated, encrypted connections. When combined with SPF, DKIM, DMARC, and TLS Reporting, it forms part of a comprehensive email security strategy that helps protect sensitive information, strengthen customer trust, and reduce organizational risk.

For businesses that value secure communication, MTA-STS is no longer just a technical enhancement—it is an essential component of modern cyber security.

For existing Telnetworks customers, MTA-STS implementation is included as a part of the service of your Managed IT Services subscription. Contact Us now if you require more information.

Ready to Strengthen Your Email Security?

If you’re unsure whether your organisation has implemented MTA-STS correctly, please use our free to use MTA-STS checker to validate and test your MTA-STS status for your domain name.

Additionally, a professional assessment from Telnetworks can identify gaps in your DNS configuration, email authentication, and encryption policies, helping ensure your business communications remain protected against evolving cyber threats.

Lets Setup MTA-STS For Your Business

1300 700 077 • info@telnetworks.net.au

Whether you're using Microsoft 365, Google Workspace, or another enterprise email platform, implementing MTA-STS alongside SPF, DKIM, DMARC, and TLS-RPT can significantly improve your organisation's email security and resilience.