📧

SPF Checker

Sender Policy Framework (SPF) is an email authentication method used to prevent spammers from sending messages on behalf of your domain.

RFC: RFC 7208
DNS TYPE: TXT
LOOKUP LIMIT: 10 DNS lookups

What is SPF Checker?

SPF is a DNS record that lists the IP addresses or hostnames that are authorized to send email on behalf of your domain.

How it Works

When an email is received, the receiving mail server looks up the SPF record for the domain in the "Return-Path" address. If the sending server's IP is not in the list, the SPF check fails.

Key Use Cases

Preventing unauthorized servers from spoofing your domain.

Improving email deliverability to major providers like Gmail and Outlook.

Detecting "Shadow IT" sending mail without permission.

Advanced Details

SPF records have a strict limit of 10 DNS lookups. If your record uses too many "include" statements, it will break and cause authentication failures.

Cybersecurity Pros & Cons

Security Advantages
  • Explicitly whitelists authorised sending IPs — any non-listed server attempting to send on your behalf will fail SPF.
  • SPF failures feed directly into DMARC enforcement, enabling automatic quarantine or rejection of spoofed emails.
  • Detects unauthorised sending sources (shadow IT, compromised third parties) attempting to abuse your domain.
  • SPF with `-all` (hard fail) is the strongest stance — it explicitly instructs receivers to reject non-listed senders.
Security Limitations
  • SPF breaks when email is forwarded — the forwarder's IP is not in the original SPF record, causing false failures.
  • The 10 DNS lookup limit is easily exceeded in complex environments with many `include:` statements, causing PermError.
  • SPF only validates the envelope Return-Path domain, not the visible Header From — users still see a spoofed sender.
  • `~all` (softfail) is widely misused as "safe" — most providers do not reject softfail emails, rendering them ineffective.
Ready to Test?

Use our professional-grade tool to perform a real-time check for this module.

Run Module Now
Related Docs