Why validate SPF syntax before publishing?
A malformed SPF (Sender Policy Framework) record can have immediate consequences: rejected emails, disabled authentication, or worse, a false sense of security. Syntax validation catches these problems before they impact your deliverability.
Three main use cases:
- New SPF -> Validate structure before first publication
- SPF modification -> Verify that changes don't introduce errors
- Deliverability diagnosis -> Confirm that syntax isn't causing rejections
How to use the validator in 3 steps
Step 1: Copy the SPF record
Retrieve your record from:
- Your DNS interface (GoDaddy, Cloudflare, Route 53, etc.)
- A DNS lookup tool
- Directly from your text editor if you're writing it
Expected format:
v=spf1 ip4:203.0.113.0/24 include:_spf.google.com -all
Step 2: Paste into the validator
Paste the complete record into the form above. The tool automatically analyzes:
- ✅ Base structure (v=spf1)
- ✅ Mechanisms (ip4, ip6, mx, a, include, exists, ptr)
- ✅ Modifiers (redirect, exp)
- ✅ Qualifiers (+, -, ~, ?)
- ✅ Final directive (all)
Step 3: Fix and publish
The report displays:
- Errors (red): Blocking issues to fix
- Warnings (orange): Security risks or best practices
- Information (blue): Details about the analyzed structure
Fix the errors, then publish to your DNS.
What is SPF syntax?
An SPF record is a character string published in a DNS TXT record. Its syntax follows a precise structure defined by RFC 7208:
v=spf1 [qualifier]mechanism [modifier] ... final_directive
Components:
| Element | Examples | Role |
|---|---|---|
| Version | v=spf1 | Required, always first |
| Qualifier | +, -, ~, ? | Determines action (pass, fail, softfail, neutral) |
| Mechanism | ip4:, mx, include:, a: | Defines authorized senders |
| Modifier | redirect=, exp= | Additional options |
| Final directive | -all, ~all, ?all | Default action for non-matches |
What exactly does the validator analyze?
Syntax errors
| Error code | Description | Impact |
|---|---|---|
missing_version | Missing v=spf1 | SPF ignored (permerror) |
unknown_mechanism | Unrecognized mechanism | Invalid SPF |
mechanism_missing_value | include: without domain | Invalid SPF |
mechanism_invalid_value | Malformed IP or CIDR | Invalid SPF |
duplicate_modifier | Two redirect= | Invalid SPF |
multiple_all | Multiple all directives | Invalid SPF |
Security warnings
| Code | Description | Risk |
|---|---|---|
weak_qualifier | ?all (neutral) | No protection |
permissive_all | +all | Authorizes everyone |
softfail_all | ~all without transition to -all | Partial protection |
DNS limits
| Code | Description | RFC limit |
|---|---|---|
lookup_limit_exceeded | More than 10 DNS lookups | 10 max |
void_lookup_limit_exceeded | Too many void responses | 2 max |
lookup_cycle | Reference loop | Forbidden |
Concrete use cases
Case 1: New domain, first SPF
Situation: You're setting up email for captaindns.com with Google Workspace.
Action: Validate before publishing:
v=spf1 include:_spf.google.com -all
Expected result:
- ✅ Valid syntax
- ✅ 1 DNS lookup (under the 10 limit)
- ✅ Strict final directive (-all)
Case 2: Adding a new marketing service
Situation: You're adding Mailchimp to your existing SPF.
Current SPF:
v=spf1 include:_spf.google.com -all
Modified SPF:
v=spf1 include:_spf.google.com include:servers.mcsv.net -all
Validation: Confirm that the addition doesn't exceed 10 lookups and that the syntax remains valid.
Case 3: "permerror" in production
Symptom: Your emails fail with SPF permerror.
Diagnosis: Paste the record into the validator.
Detected error:
v=spf1 ip4:192.168.1.1 include: -all
Error: mechanism_missing_value - include: without domain.
Fix:
v=spf1 ip4:192.168.1.1 include:_spf.captaindns.com -all
Case 4: Too many DNS lookups
Symptom: The validator shows lookup_limit_exceeded.
Diagnosis: Your SPF has too many includes:
v=spf1 include:_spf.google.com include:spf.protection.outlook.com include:amazonses.com include:_spf.salesforce.com include:sendgrid.net include:mailchimp.com -all
Solutions:
- Replace some includes with direct ip4/ip6
- Use a dedicated subdomain (e.g.,
marketing.captaindns.com) - Remove unused services
- Use our SPF Flattener to automatically resolve includes into IPs
FAQ - Frequently asked questions
Q: What is an SPF record?
A: SPF (Sender Policy Framework) is a DNS TXT record that lists servers authorized to send emails for your domain. Format: v=spf1 followed by mechanisms (ip4, mx, include) and a final directive (-all, ~all).
Q: Why validate SPF syntax before publishing?
A: A malformed SPF record generates a permanent error (permerror) that can reject all your emails or completely disable SPF verification. Validating before publishing prevents service interruptions.
Q: What is the DNS lookup limit for SPF?
A: RFC 7208 limits SPF evaluation to 10 DNS lookups. Each include, a, mx, ptr and exists counts. Exceeding this limit generates a permerror and may fail authentication.
Q: What does the qualifier -all vs ~all mean?
A:
-all(hard fail): Rejects unauthorized emails~all(soft fail): Marks as suspicious but accepts
Start with ~all for testing, then switch to -all in production for maximum protection.
Q: How do I fix the "too many DNS lookups" error?
A:
- Replace includes with direct
ip4/ip6 - Remove unused mechanisms
- Use subdomains with their own SPF
- Avoid
ptr(deprecated and costly in lookups)
Q: Can I have multiple SPF records?
A: No. The RFC requires a single SPF record per domain. Multiple records generate a permerror. Merge your policies into one TXT starting with v=spf1.
Q: Does the tool validate included domains?
A: The validator checks the syntax of domains referenced by include and redirect. For complete analysis with DNS resolution and recursive lookup counting, use the SPF Inspector.
Complementary tools
| Tool | Purpose |
|---|---|
| SPF Inspector | Analyze a published SPF with complete DNS resolution |
| SPF Flattener | Flatten your SPF to stay under the 10 DNS lookup limit |
| DKIM Inspector | Validate your DKIM signature |
| DMARC Inspector | Configure and test your DMARC policy |
| Email Header Analyzer | Diagnose SPF/DKIM/DMARC on a received email |
Useful resources
- RFC 7208 - Sender Policy Framework (official SPF specification)
- Google - Set up SPF (Google Workspace guide)
- Microsoft - SPF for Microsoft 365 (Outlook/M365 guide)