Eligible for MTA-STS but not configured
`your domain` already enforces DMARC (p=quarantine or reject), so the domain authenticates who is allowed to send as it — but nothing stops a network attacker from downgrading an otherwise-encrypted delivery to your domain to plaintext SMTP, since opportunistic TLS falls back silently.
Why it matters
`your domain` already enforces DMARC (p=quarantine or reject), so the domain authenticates who is allowed to send as it — but nothing stops a network attacker from downgrading an otherwise-encrypted delivery to your domain to plaintext SMTP, since opportunistic TLS falls back silently. MTA-STS tells senders to require TLS to your exact MX hosts or refuse delivery, closing that gap. Optional hardening once your mail authentication is already correct, not a fix for a bug.
How ShipReady detects it
Email-authentication DNS records (DMARC / SPF). Almost every AI-built SaaS sends transactional email — password resets, magic links, receipts — through Resend, SendGrid or Postmark. Setting that up gets the mail delivered; it does not stop anyone else sending mail that claims to come from the same domain. Without a DMARC policy, a receiving server has no instruction to reject a forgery, so an attacker can send "reset your password" from the product's own domain and the message will land in the inbox looking authentic. This check is almost entirely DNS rather than HTTP — one exception is MTA-STS, whose policy is only half-published in DNS; the other half is a file fetched over HTTPS (see _check_mta_sts). Nearly everything else here is the most deterministic kind of check the scanner has: a record either exists or it does not, so there is no heuristic and no false-positive surface. The one place judgement is required is deciding WHICH domain to ask about — see _organizational_domain.
Detection is deterministic. ShipReady reports this only when it observes the condition directly, and prefers to miss a real problem over inventing one. Rule version 1.10.0.
How to fix it
This is the prompt ShipReady puts in your report — written to be pasted straight into Cursor, Claude Code, or whichever assistant built the app.
your domain already enforces DMARC, which is the harder prerequisite — MTA-STS is the next step, and it's mostly configuration rather than code. Publish a TXT record at _mta-sts.your domain with the value "v=STSv1; id=<a string you change each time you update the policy, e.g. a timestamp>". Then host a policy file over HTTPS at https://mta-sts.your domain/.well-known/mta-sts.txt containing: "version: STSv1", "mode: testing" (start here, not enforce), one "mx:" line per hostname in your MX record, and "max_age: 604800". Watch for delivery problems for a few weeks, then switch mode to enforce.
Frequently asked questions
- What does "Eligible for MTA-STS but not configured" mean?
- `your domain` already enforces DMARC (p=quarantine or reject), so the domain authenticates who is allowed to send as it — but nothing stops a network attacker from downgrading an otherwise-encrypted delivery to your domain to plaintext SMTP, since opportunistic TLS falls back silently.
- How serious is it?
- ShipReady rates this low. Worth fixing. Small individually, and they accumulate.
- How do I fix it?
- Paste the fix prompt on this page into Cursor, Claude Code or your AI editor. It is the same prompt ShipReady puts in your report.
- Can I check my own site?
- Yes — ShipReady scans up to ten pages of any public site for free and reports this alongside every other check. The free report lists every issue it finds and shows full evidence and a fix prompt for the critical and high-severity ones; medium and low findings are counted and unlock on Pro.
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