Enhancing Email Security with MTA-STS and TLS-RPT

Hayden Kirk

May 20, 2024

Adding to our previous post on email security we are now shifting the focus to more advanced topics, MTA-STS and LTS-RPT.

The security of email communications is paramount, especially for large enterprises and government agencies handling sensitive information. Two protocols, MTA-STS (Mail Transfer Agent Strict Transport Security) and TLS-RPT (Transport Layer Security Reporting) offer robust solutions to enhance email security.

MTA-STS is a security standard that ensures the secure transmission of emails over an encrypted SMTP connection. The acronym MTA stands for Message Transfer Agent, which is a program that transfers email messages between computers. The acronym STS stands for Strict Transport Security, which is the protocol used to implement the standard. An MTA-STS-aware mail transfer agent (MTA) or secure message transfer agent (SMTA) operates per this specification and provides a secure end-to-end channel for sending email over unsecured networks.

The MTA-STS protocol allows an SMTP client to verify the server identity and ensure that it is not connecting to an impostor by requiring the server to provide its certificate fingerprint in the TLS handshake. The client then verifies the certificate against a trust store containing certificates of known servers.

The History of MTA-STS

In the year 1982, SMTP was first specified and it did not contain any mechanism for providing security at the transport level to secure communications between the mail transfer agents. However, in 1999, the STARTTLS command was added to SMTP that in turn supported the encryption of emails between the servers, providing the ability to convert a non-secure connection into a secure one that is encrypted using TLS protocol.

However, it’s taken many years for encrypted email to be implemented across organisations because of the complexity of implementation.

Why MTA-STS is Crucial

Protecting Sensitive Data: MTA-STS enforces secure connections between mail servers, ensuring that emails are transmitted over encrypted channels. This prevents unauthorized interception and tampering, safeguarding sensitive information from cyber threats such as man-in-the-middle attacks.

Building Trust and Compliance: Implementing MTA-STS demonstrates a commitment to high-security standards, fostering stakeholder trust. It helps organisations comply with stringent data protection regulations, avoiding potential legal and financial repercussions.

The Role of TLS-RPT

Enhanced Visibility: TLS-RPT provides detailed reports on issues encountered during email transmission. This visibility allows organisations to identify and address vulnerabilities promptly, ensuring the continuous security of their email systems.

Proactive Security Management: Organisations can take proactive measures to rectify misconfigurations and prevent security breaches by receiving regular reports on transmission failures. This proactive approach is crucial for maintaining the integrity of email communications.

Importance for Large Enterprises and Government Agencies

Data Protection: For organisations handling large volumes of sensitive data, securing email communications is non-negotiable. MTA-STS and TLS-RPT provide an additional layer of security, ensuring that data remains confidential and secure.

Regulatory Compliance: Compliance with data protection laws and regulations is essential for avoiding penalties and maintaining operational legitimacy. Implementing these protocols helps meet compliance requirements effectively.

Operational Continuity: Secure and reliable email communication is vital for operational efficiency. By ensuring emails are securely transmitted and potential issues are promptly addressed, organizations can maintain seamless communication channels.

Enhanced Trust: Implementing robust email security measures builds trust with clients, partners, and stakeholders. It reassures them that the organization prioritizes the security of their communications and data.


For large enterprises and government agencies, the implementation of MTA-STS and TLS-RPT is not just a technical upgrade; it’s a strategic necessity. These protocols provide crucial security enhancements, ensuring that email communications are secure, compliant, and reliable.

At Layer3, we specialise in helping organisations implement these advanced security measures, safeguarding their email communications and building trust with their stakeholders.

More often, potential customers are looking at the security of your organisation before they engage with you. It’s also important to have visibility across your email service. More often than not, organisations have no idea how their email service is performing. As part of our email monitoring service, we also implement and monitor MTA-STS and TLS-RPT.

For more information on enhancing your email security, contact us.

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