Mail Transfer Agent Strict Transport Security (MTA-STS) is a crucial security standard designed to protect email in transit. It ensures that when other mail servers send email to your domain, they do so over a secure, encrypted TLS connection, preventing eavesdropping and man-in-the-middle attacks. A key part of MTA-STS is the policy file, a simple text file you host on a web server. This file tells sending servers what your security requirements are. For this entire system to function correctly, your web server must respond with the right HTTP status code when a sending server requests your policy file. It's a small technical detail, but it makes all the difference.
The required status code for an MTA-STS policy
The correct and required HTTP status code for a successfully retrieved MTA-STS policy file is 200 OK. This is not just a suggestion or a best practice; it's a mandatory requirement outlined in the official standard, RFC 8461. When a mail server requests your policy, a 200 OK response indicates that the request was successful and the policy is contained in the response body.
Why a 200 OK is necessary
To understand why this specific code is required, think of the process. A remote mail server acts as a client. It makes an HTTPS GET request to a very specific URL: https://mta-sts.yourdomain.com/.well-known/mta-sts.txt. Your web server, which hosts this file, must respond to this request. A 200 OK is the universal signal for "I have found what you asked for, and here it is." Any other response code signals a problem or a different outcome, which will cause the sending server to ignore your policy.
Using an incorrect status code can lead to several problems:
- Policy is ignored: If your server returns a 404 Not Found, 500 Server Error, or even a 301 Moved Permanently redirect, the sending MTA will treat your policy as unavailable. It will not follow redirects.
- Caching problems: MTA-STS policies are cached by senders for a duration specified within the policy itself. An improper status code can disrupt this caching behavior, causing inconsistent policy enforcement.
- Security is compromised: If your policy cannot be fetched, sending servers may fall back to sending email over unencrypted connections, defeating the entire purpose of MTA-STS and leaving your communications vulnerable.
The standards bodies that create internet protocols, like the IETF, are strict about these details to ensure that systems built by different companies all over the world can communicate reliably. In short, to properly implement MTA-STS, you must ensure your web server configuration returns a 200 OK for your policy file. It's a simple, non-negotiable step for securing your email.
What is the file name for an MTA-STS policy?
What DNS record type is used for MTA-STS policy discovery?
What is the 'version' field in an MTA-STS policy?
What port does MTA-STS typically use for policy fetching?
What is the 'mode' field in an MTA-STS policy?
What is the directory path for the MTA-STS policy file?
