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DANE-for-SMTP-how-to.md
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- Automated monitoring of your own email servers and related DNS records is a must.
- Robust automation of coordinated DNS and email server certificate chain updates.
- These topics will be covered in more detail below.
* Please deploy DNSSEC, and DANE for your email servers, but plan carefully. Botched deployments not only harm the domain in question, but also have a deterrent effect on adoption by others.
* Please plan carefully and then deploy DANE for your email servers. Botched deployments not not only harm the domain in question, but also have a deterrent effect on adoption by others.
# Introduction
This how-to is created by the Dutch Internet Standards Platform (the organization behind [internet.nl](https://internet.nl)) and is meant to provide practical information and guidance on implementing DANE for SMTP.
# What is DANE?
DANE is short for "**D**NS-based **A**uthentication of **N**amed **E**ntities" and is described in [RFC 6698](https://tools.ietf.org/html/rfc6698) and [RFC 7671](https://tools.ietf.org/html/rfc7671). DANE enables publication in secure DNS of keys and certificates for use with TLS. DANE TLSA records published in the server operator's signed DNS zone provide a downgrade-resistant means to discover support for STARTTLS and to validate the server's certificate chain without relying on additional trusted parties outside the delegation chain in DNS.
DANE is short for "**D**NS-based **A**uthentication of **N**amed **E**ntities" and is described in [RFC 6698](https://tools.ietf.org/html/rfc6698) and [RFC 7671](https://tools.ietf.org/html/rfc7671). DANE establishes a downgrade-resistant method to verify an SMTP servers identity **before** it starts to transport an email message over a STARTTLS encrypted layer. In order to achieve this it uses verification information retrieved from the recipients DNSSEC signed DNS zone. DANE does not rely on additional trusted parties outside the delegation chain in DNS.
DANE is designed to work with any TLS service, not just email, but DANE for HTTP is not presently supported by the major browsers and so has seen little deployment. DANE for SMTP (which is described in [RFC 7672](https://tools.ietf.org/html/rfc7672) on the other hand, is used increasingly and adds active attack (man-in-the-middle) resistance to SMTP transport encryption [RFC 7672 Section 1.3](https://tools.ietf.org/rfc7672#section-1.3). DANE for SMTP uses the presence of DANE TLSA records to securely signal TLS support and to publish the means by which SMTP clients can successfully authenticate legitimate SMTP servers. The result is called "opportunistic DANE TLS", and resists downgrade and man-in-the-middle (MITM) attacks when the destination domain and its MX hosts are DNSSEC signed, and TLSA records are published for each MX host.
DANE, as a method, has been designed to work with any TLS service. DANE for SMTP (which is described in [RFC 7672](https://tools.ietf.org/html/rfc7672) implements the DANE method for SMTP. It is used increasingly and adds active attack (man-in-the-middle) resistance to SMTP transport encryption [RFC 7672 Section 1.3](https://tools.ietf.org/rfc7672#section-1.3). DANE for SMTP uses the presence of DNS TLSA ressource records to securely signal TLS support and to publish the means by which SMTP clients can successfully authenticate legitimate SMTP servers. The result is called "opportunistic DANE TLS", and resists downgrade and man-in-the-middle (MITM) attacks when the destination domain and its MX hosts are DNSSEC signed, and TLSA records are published for each MX host. While possible, DANE for HTTP is not presently supported by the major browsers and so has seen little deployment.
# Why use DANE for SMTP?
DANE offers several advantages by binding X.509 certificates to domains using DNSSEC. In an SMTP context this allows sending e-mail servers to verify the autenticity of the offered certificate by the receiving domain's e-mail server. This helps to address risks that occur when using TLS connections between e-mail servers.