I learned the hard way that great content can still land in junk if my email authentication isn’t watertight. When I’m protecting a brand’s domain and chasing consistent email delivery, I start with the basics: the Sender Policy Framework. If you need a quick refresher on what SPF is and how it fits into email authentication protocols, this primer on the Sender Policy Framework is a solid grounding. In my day-to-day, an SPF checker is my diagnostic tool, my pressure gauge, and my early-warning system for authentication issues. It helps me validate DNS records, spot misconfigurations, and keep email security tight against phishing and email spoofing.
I also keep a shortlist of trusted tools. I’ll run an SPF record check with MxToolBox (their SPF checker is fast and visual), and I like how EasyDMARC frames an SPF lookup alongside DMARC and DKIM workflows. For deeper diagnostics, I’ll cross-check with PowerDMARC’s SPF record lookup or dmarcian’s thoughtful SPF survey. Between those and a practical validator like Kitterman’s SPF validator, I can triage 90% of SPF errors in minutes.
Get your foundations right (Tips 1–3)
Tip 1: Verify your current SPF record and syntax with a reputable checker
My first pass is boring—and that’s the point. I confirm there’s a single v=spf1 TXT record for the domain and that every mechanism parses cleanly. A good SPF validator will flag deprecated constructs (like ptr), typos in mechanisms (ip4/ip6, a, mx, include, exists), funky qualifiers, and formatting limits. I’ve seen a stray space or an extra quote nuke email deliverability for weeks.
- I run an SPF record lookup and compare results across tools; discrepancies often reveal hidden DNS lookup or caching issues.
- I do a straight SPF validation to ensure the include chain resolves and we’re not flirting with the 255-character line or 512-byte DNS packet thresholds.
- If I see multiple SPF records (classic permerror), I consolidate into a single authoritative SPF record.
Quick syntax triage
I scan for:
- Deprecated ptr and +all (security risk, tanking domain reputation)
- Invalid CIDRs or malformed mechanisms
- Redundant a/mx mechanisms when I’m not sending from the root host or MX
Mechanism sanity check
If a mechanism isn’t needed for email delivery, it’s dead weight. I remove it. That one change often reduces lookups and fixes later diagnostics.
I inventory every system that sends on behalf of the domain: ESPs, CRMs, ticketing platforms, marketing automation, gateways—plus oddballs like EasySender, Touchpoint notices, and internal tooling. Then I use an SPF checker to test each vendor’s includes and the authorized IP addresses they publish. My rule: every legitimate sender passes; unknown sources fail.
- I keep a spreadsheet with vendor names, include domains, IP addresses, and TTLs. Sounds old school, but it saves me when a provider silently changes ranges.
- I run targeted SPF record check tests using the checker’s “hypothetical sender” or email header analyzer functions (when available) to catch authentication issues before they hit production.
- If we’re onboarding a new tool, I evaluate its guidance and reputation—reviews on places like G2 Crowd, SourceForge, Channel Program, or Expert Insights help me gauge support maturity and risk.
For flattening and quick sanity checks on smaller stacks, I sometimes reach for AutoSPF’s SPF checker. It’s handy when I need a second opinion and a clear view of include behavior.
Tip 3: Control DNS lookups—flatten and prune to stay under the 10-lookup limit
SPF has a hard cap of 10 DNS lookups. I treat that as sacred. I use the checker’s lookup counter to spot heavy include chains, prune unused vendors, and replace nested includes with flattened IPs when necessary. I’m ruthless about avoiding unnecessary a and mx mechanisms, and I never use ptr.
- I validate results across multiple tools—DNSChecker’s SPF record validation is great for catching regional propagation quirks.
- If I flatten, I record the source includes and note the vendor’s change cadence so I can refresh ranges proactively.
Flattening safely
Flattening too aggressively is a compliance and maintenance trap. When I must flatten:
- I keep the original include in comments for documentation and reporting.
- I check vendor status pages or MSP Program updates regularly.
- I schedule a recurring risk assessment to revisit whether flattening is still appropriate.
TTL hygiene
I tune TTLs so updates don’t take forever to propagate. After edits, I monitor with a domain scanner mindset—query multiple resolvers and verify that DNS records reflect my changes before I tighten policies.
Tighten enforcement and alignment (Tips 4–5)
Tip 4: Choose the right enforcement qualifier (~all vs -all) and test before tightening
I don’t jump to -all on day one. I start with ~all (soft fail), validate all legitimate senders through repeated SPF record check runs, and simulate results for known and unauthorized IPs. Once monitoring shows clean passes and no false fails, I move to -all for stronger protection.
- I’ll dry-run using a combination of the checker and a staging environment so I know how messages will route.
- Power users: the dmarcian SPF survey style of visualization helps me explain to stakeholders why we’re tightening.
“Dry-run” enforcement
Before flipping to -all, I cross-verify with MxToolBox or Kitterman, then spot-check a few recipients for bounces and spam-folder behavior. I also glance at blacklists and broader diagnostics just to ensure no unrelated factor masks SPF results.
Tip 5: Check SPF alignment with DMARC and subdomain policies
SPF alone doesn’t guarantee DMARC pass; alignment matters. I use a checker that calls out alignment between the Mail From (Return-Path) and the visible From domain. If I’m authenticating a delegated sender on a subdomain, I test both the organizational domain and subdomain to ensure sp= policies and redirects don’t break alignment.
- If forwarding or list servers rewrite the envelope, I expect SPF to fail and rely on DKIM for DMARC pass. That’s by design, not a bug.
- I sanity-check BIMI ambitions early—no point chasing logos if DMARC alignment can’t hold across flows.
- For admin workflows, EasyDMARC’s SPF lookup and MxToolBox’s views combine nicely with a DMARC reporting dashboard like Delivery Center for monitoring.
Diagnose and monitor like a pro (Tips 6–7)
Tip 6: Use the checker to diagnose common SPF errors and edge cases
I’ve seen every flavor of SPF errors under the sun:
- Multiple SPF records (permerror)
- Nonexistent includes
- Too-many-lookups
- Invalid CIDRs or mechanism order mishaps
- +all misconfigurations that invite email-based threats
I test mailing lists, forwarders, and gateways to understand when SPF will predictably fail—and when DKIM needs to carry DMARC. For gnarly cases, I compare the outputs of a strict validator like Kitterman’s SPF validator with MxToolBox and PowerDMARC’s SPF record lookup. If three tools disagree, that’s my cue to dig into raw DNS lookup responses, perform a fresh SPF record lookup, and review the checker’s diagnostics and reporting for hints. When the puzzle persists, I’ll also reference tooling like dmarcian’s SPF survey for structural insight.
Pro tip: a reputable SPF record generator can help rebuild cleanly after a complex migration, but I still validate every hop with an SPF checker before publishing.
Tip 7: Monitor changes over time—and automate what you can
The vendors change; IP addresses change; include targets change. I set calendar reminders to re-run an SPF record check monthly, and I always recheck after onboarding a new platform. I’ve had marketers add a “quick” integration on a Friday and unintentionally crater email deliverability by Monday.
- I use tool APIs or CI/CD hooks where available so infrastructure changes trigger an immediate SPF validation.
- I log edits with timestamps, TTLs, and rationale—future me loves that documentation.
- I pair SPF monitoring with DMARC aggregate reporting, periodic domain reputation checks, and a lightweight compliance check to keep protection strong.
When I want a different view—for example, how a vendor’s include expands across regions—I’ll spin up an SPF lookup in MxToolBox and mirror it with an EasyDMARC lookup for comparison. If results get weird, a secondary perspective from DNSChecker’s validation helps me spot propagation timing. And when I need to explain SPF’s mechanics or limitations to stakeholders, I often reference a clear, tool-neutral video explanation—it keeps the conversation grounded while we make measured changes.
