---
description: Cloudflare Email Security now supports post-quantum hybrid key exchange on inbound and outbound SMTP connections.
title: Post-quantum key exchange for MX deployments
image: https://developers.cloudflare.com/changelog/post/2026-08-17-post-quantum-key-exchange-mx/og.png?v=68a4c51489d38a1d
---

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August 17, 2026

## Post-quantum key exchange for MX deployments

[Email security](https://developers.cloudflare.com/cloudflare-one/email-security/)

Copy as Markdown| [View as Markdown](https://developers.cloudflare.com/changelog/post/2026-08-17-post-quantum-key-exchange-mx/index.md)| [Agent setup](https://developers.cloudflare.com/agent-setup/)

Cloudflare Email Security now supports post-quantum hybrid key exchange with X25519MLKEM768 on the SMTP connections we make to receive and deliver mail. Deploying Email Security in front of a provider that supports post-quantum hybrid key agreement (like Google Workspace) will create a TLS 1.3 connection using post-quantum key agreement.

Inbound MX connections and outbound delivery connections now negotiate the [X25519MLKEM768](https://developers.cloudflare.com/ssl/post-quantum-cryptography/#hybrid-key-agreement) hybrid key agreement when the peer supports it, protecting SMTP traffic against [harvest-now, decrypt-later ↗︎](https://blog.cloudflare.com/pq-2024/) attacks.

Support is backwards compatible and enabled automatically for all customers. Senders and receivers that do not yet advertise post-quantum key agreement continue to connect with classical key exchange.

This applies to all Email Security packages:

- **Advantage**
- **Enterprise**
- **Enterprise + PhishGuard**

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