Official Setup Guides
For step-by-step instructions, check out these official guides from the source:
What is MTA-STS?
MTA-STS (Mail Transfer Agent Strict Transport Security) is an email security protocol that enforces encrypted connections when email is transmitted between mail servers. Without MTA-STS, attackers can intercept emails in transit by downgrading the connection from encrypted (TLS) to unencrypted.
Think of it as HTTPS for email transport—it ensures your order confirmations, shipping notifications, and customer communications travel securely from your email provider to your customers’ inboxes.
Why MTA-STS Matters for Shopify Merchants
Your Shopify store sends sensitive emails daily:
- Order confirmations with customer addresses and order details
- Shipping notifications with tracking information
- Password reset links that could compromise accounts
- Customer support responses with personal information
Without MTA-STS, these emails can be intercepted on public networks. Attackers could:
- Read customer order details and personal information
- Modify emails to include phishing links
- Steal password reset tokens to hijack accounts
- Impersonate your brand with real customer data
How MTA-STS Works
MTA-STS operates in three parts:
1. DNS Record Declaration
A DNS TXT record at _mta-sts.yourdomain.com announces that your domain supports MTA-STS and provides a policy ID.
2. Policy File
A text file hosted at https://mta-sts.yourdomain.com/.well-known/mta-sts.txt specifies:
- Which mail servers handle your email
- Whether to enforce or just test the policy
- How long the policy should be cached
3. TLS Reporting (TLS-RPT)
A DNS record at _smtp._tls.yourdomain.com tells mail servers where to send reports about TLS connection success or failures.
The Shopify Challenge
Here’s the catch: Shopify doesn’t allow you to host arbitrary files on your domain. The MTA-STS policy file must be accessible at a specific URL (/.well-known/mta-sts.txt), but Shopify’s platform doesn’t support creating this directory structure.
This means Shopify merchants need alternative hosting solutions for the policy file.
Setup Options for Shopify Stores
Option 1: Cloudflare (Recommended)
If you use Cloudflare for DNS:
- Create a CNAME record:
_mta-stspointing to_mta-sts.mx.cloudflare.net(proxy disabled) - Add a TXT record at
_mta-stswith your policy ID - Cloudflare handles the policy file hosting automatically
Option 2: GitHub Pages (Free)
- Create a GitHub repository for your MTA-STS policy
- Add a file at
/.well-known/mta-sts.txtwith your policy - Configure GitHub Pages with custom domain
mta-sts.yourdomain.com - Enable HTTPS in repository settings
Option 3: Firebase Hosting (Free)
- Set up a Firebase project
- Deploy your MTA-STS policy file to Firebase
- Connect the custom domain
mta-sts.yourdomain.com - Firebase provides automatic SSL
MTA-STS Policy Modes
| Mode | Behavior | When to Use |
|---|---|---|
testing | Report failures but deliver anyway | Initial setup, monitoring |
enforce | Reject emails if TLS fails | After confirming everything works |
none | Disable the policy | Troubleshooting, disabling |
Start with testing mode to catch configuration issues before they affect email delivery.
What Recon Detects
Recon monitors your MTA-STS configuration and alerts you to:
| Issue | Severity | Description |
|---|---|---|
| MTA-STS missing | Medium | No MTA-STS policy configured |
| Policy file inaccessible | Medium | Can’t reach the policy file URL |
| Invalid policy syntax | Medium | Policy file has configuration errors |
| Testing mode only | Low | Consider upgrading to enforce mode |
How Recon Helps
Recon validates your email transport security by:
- Checking for MTA-STS DNS records and policy files
- Verifying TLS-RPT reporting is configured
- Alerting you to misconfigurations before they cause problems
- Providing step-by-step guidance for different hosting setups
Priority: Medium
MTA-STS is important but not critical. Your emails will still be delivered without it—they just won’t have guaranteed encryption in transit.
Focus on DMARC, SPF, and DKIM first. Once those are solid, MTA-STS adds another layer of protection.
FAQ
Q: Will my emails fail without MTA-STS?
A: No. MTA-STS is opt-in security. Without it, email servers will still attempt TLS encryption—they just won’t require it. MTA-STS prevents downgrade attacks where attackers force unencrypted connections.
Q: Does Shopify support MTA-STS natively?
A: Not directly. Shopify doesn’t allow hosting the required policy file. You’ll need to use Cloudflare, GitHub Pages, Firebase, or another hosting solution for the mta-sts subdomain.
Q: How long does MTA-STS take to set up?
A: With Cloudflare, about 10 minutes. With GitHub Pages or Firebase, 30-60 minutes including DNS propagation.
Q: Is MTA-STS required by Gmail or Yahoo?
A: No. Unlike DMARC, MTA-STS is not mandated by major email providers. However, it’s increasingly recommended as a best practice for email security.
External Resources
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