Email deliverability bugs are notorious because they rarely fail loudly in staging. A domain can have a syntactically valid TXT record in Cloudflare or Route53 while Gmail, Yahoo, and Exchange Online silently downgrade its messages to Spam due to three classic configuration traps.
Trap 1: The RFC 7208 SPF 10-DNS-Lookup Limit (PermError)
Under RFC 7208 Section 4.6.4, a receiving mail server is only permitted to perform at most 10 DNS-querying mechanisms (include, a, mx, ptr, exists, redirect) when evaluating your SPF record—including all nested include: chains!
Watch how quickly a typical growing SaaS company blows past 10 lookups:
include:_spf.google.com(Google Workspace) → 3–4 lookupsinclude:spf.protection.outlook.com(Microsoft 365) → 2 lookupsinclude:sendgrid.net→ 1–2 lookupsinclude:servers.mcsv.net(Mailchimp) +include:mail.zendesk.com+mx→ 5+ lookups
Once the cumulative count hits 11, strict receivers abort SPF evaluation with spf=permerror. Note that ip4: and ip6: CIDR mechanisms cost 0 DNS lookups.
Trap 2: p=none Without an Aggregate Reporting Mailbox (rua=)
Since the 2024–2026 Gmail and Yahoo bulk-sender mandates, publishing v=DMARC1; p=none; without a valid rua=mailto:... tag gives you zero visibility into spoofing and zero enforcement. Worse, if your subdomain policy (sp=) is omitted under p=none, attackers can spoof arbitrary subdomains (billing.yourdomain.com) with impunity.
Trap 3: Using ~all or ?all Instead of -all
Neutral (?all) provides zero protection, and reckless +all effectively authorizes the entire internet to send mail on behalf of your domain. Once all legitimate ESPs are inventoried and DKIM signing is active, transitioning to -all (HardFail) paired with p=quarantine or p=reject locks the door.
Test Your Domain Instantly
You can audit any domain's live MX, SPF, DMARC, DKIM, and MTA-STS posture—or generate a lookup-budgeted SPF + DMARC record set—using our Free DMARC, SPF & MTA-STS Checker (/tools/email-dns-checker), powered by POST /v1/email-dns and POST /v1/email-dns-generator.