Simple Authentication and Security Layer (SASL)

What Is SASL?

SASL (Simple Authentication and Security Layer) is a framework used by internet protocols to handle authentication and, in some cases, encryption. It provides a standardized way for clients and servers to verify user identities securely when establishing a connection.

In email, SASL is commonly used during the SMTP and IMAP processes to ensure that only authorized users can send or retrieve messages.

How Does SASL Work?

SASL acts as a flexible layer between an application protocol (like SMTP) and an authentication mechanism (such as plain text passwords or OAuth).

Here’s how it typically functions in an email context:

1. The client (like an email app or mail relay) connects to the mail server.
2. The server announces the SASL mechanisms it supports (for example, PLAIN, LOGIN, CRAM-MD5, or OAUTHBEARER).
3. The client selects a method and provides credentials.
4. The server validates those credentials before allowing the session to proceed.

Because SASL is modular, new authentication methods can be added without changing the protocols themselves. This flexibility makes it widely used across email, messaging, and directory services.

SASL in Email Security and Delivery

SASL plays a crucial role in controlling who can send mail through a mail server. It prevents unauthorized use of mail relays, which are often targeted by spammers.

Although SASL operates before SPF, DKIM, and DMARC validation, it complements them by establishing authenticated connections for legitimate senders. Once an email is accepted via SASL authentication, the message can then be checked for additional domain-level authenticity through those other protocols.

Many organizations also use SASL with Transport Layer Security (TLS) to encrypt the login process and protect user credentials during transmission.

SASL and DMARCeye

DMARCeye focuses on domain-level authentication, while SASL operates at the session level. However, the two contribute to the same goal: ensuring that all emails come from verified and authorized sources.

By analyzing DMARC aggregate reports, DMARCeye can reveal when emails originate from mail servers that use proper authentication practices, including SASL-secured submission systems. Together, these layers build a strong, end-to-end framework for secure and trustworthy email communication.