ip4: SPF Mechanism

The SPF ip4 mechanism explicitly authorises an IPv4 address or CIDR range to send email. No DNS lookup required, the most efficient SPF mechanism.

Type
Mechanism
Syntax
ip4:<ip-address>[/prefix-length]
DNS Lookup
No (no extra lookup)
Example
ip4:203.0.113.0/24

💬 What This Mechanism Does

The ip4 mechanism directly authorises an IPv4 address or CIDR subnet. It requires no DNS lookup, so it doesn't count against the 10-lookup limit. Use it for dedicated servers or static SMTP relay IPs that you control.

When to Use This

  • A dedicated outbound SMTP relay with a static IP (ip4:198.51.100.5)
  • An on-premise mail server subnet (ip4:192.0.2.0/24)
  • A transactional email service that provides a fixed IP range

⚠️ Watch Out For

  • Does not count toward the 10-lookup limit. Use ip4/ip6 over include where possible.
  • Avoid ranges larger than /24 unless you genuinely own the whole subnet.

📚 RFC References

↗RFC 7208 §5.6: The "ip4" and "ip6" Mechanisms

🔗 Related SPF Elements

ip6
Mechanism
 include
Mechanism
 a
Mechanism

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