DNS Lookups for Email Deliverability Troubleshooting

The DNS Records That Control Email Delivery

Four DNS record types determine whether your email reaches the inbox or spam folder:

Diagnosing Delivery Problems

Step 1 — Check MX Records

curl -X POST https://api.toolkitapi.io/v1/devtools/dns-lookup \
  -H "X-API-Key: $API_KEY" \
  -d '{"domain": "example.com", "type": "MX"}'

Missing MX records mean no mail server exists to receive your email.

Step 2 — Validate SPF

An SPF record is a TXT record starting with v=spf1. It should include every IP or service that sends on your behalf:

v=spf1 include:_spf.google.com include:sendgrid.net ~all

~all (softfail) is more permissive than -all (hardfail). Use -all for tighter security.

Step 3 — Confirm DKIM

DKIM records live at <selector>._domainkey.<domain>. If you don't know your selector, check your email provider's setup guide.

Step 4 — Review DMARC

v=DMARC1; p=reject; rua=mailto:[email protected]

p=reject means unauthenticated emails are rejected. Start with p=none for monitoring, then graduate to quarantine and reject.

Automated Monitoring

import httpx

DOMAINS = ["example.com", "mail.example.com"]

for domain in DOMAINS:
    for rtype in ["MX", "TXT", "DKIM"]:
        r = httpx.post(
            "https://api.toolkitapi.io/v1/devtools/dns-lookup",
            headers={"X-API-Key": API_KEY},
            json={"domain": domain, "type": rtype},
        )
        records = r.json().get("records", [])
        if not records:
            print(f"WARNING: No {rtype} record for {domain}")

Run this check daily to catch DNS changes before they affect delivery.