SMX now supporting MTA-STS
We’re excited to announce that from 1st October 2025 we support MTA-STS for outbound emails. This upgrade provides a higher level of security for your messages sent to recipients who use this standard.
What’s MTA-STS?
Mail Transfer Agent Strict Transport Security (MTA-STS) is a standard that enforces the encryption of messages being sent between two mail servers. It specifies to sending servers that emails can only be sent over a Transport Layer Security (TLS) encrypted connection which prevents emails from being intercepted and / or amended by cybercriminals. (Source: Red Sift)
Essentially, it acts as a "digital policy" that tells a sending server, "You can only send me email using a secure, encrypted connection, and here is proof that you're connecting to the right server." This is widely adopted by major email providers to ensure a more secure, trusted exchange of email, and is recommended as good practice, including in the New Zealand Information Security Manual (NZISM).
What it means for you
Whilst we have always sought to send emails with encryption using opportunistic-TLS, we will now automatically apply the policy of any recipient domain that has MTA-STS enabled, ensuring your emails are only sent over an encrypted connection. While you might notice a minor delay on some deliveries as we apply the policy, this change is designed to strengthen the security of your outbound email. So there's nothing you need to do.
How you can protect your organisation with MTA-STS and SMX
We've made this change to protect outbound emails, but if you'd like to implement MTA-STS for your own domain(s), and ensure that all messages you receive are encrypted and protected from source to destination, we can help.
For customers that already subscribe to our Domain Protection Service for DMARC enforcement and compliance, MTA-STS can be set up easily through the OnDMARC portal. This covers all of the policy hosting, TLS reporting and certificate management required to enforce MTA-STS and our email security experts can guide you through this process.
If you’re interested in setting up MTA-STS policies and working towards enforcement directly, we've prepared a technical guide with all the necessary details. Reach out to our team to get a copy of the guide or download it here. As always, our email security experts are available to support you through this process.