SPF Lookup Articles

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SPF Validates the Envelope Sender, Not What You See in Your Inbox — Here's Why That Matters

SPF Validates the Envelope Sender, Not What You See in Your Inbox — Here's Why That Matters

SPF validates the envelope sender — the address used during SMTP delivery — not the "From" header address that recipients actually see. This means SPF can pass for an email that appears to be from ceo@bigcorp.com, because the attacker set a legitimate envelope sender from their own domain. Here's why DMARC's alignment requirement exists to close this gap, what -all vs ~all vs +all actually mean, and the SPF flattening trade-off.

Jun 18, 2026
SPF Mechanisms Deep Dive: How include:, mx, and Macros Each Consume Your 10-Lookup Budget

SPF Mechanisms Deep Dive: How include:, mx, and Macros Each Consume Your 10-Lookup Budget

A single `include:` mechanism can secretly consume several of SPF's 10 allowed DNS lookups, depending on what the included record itself contains. Here's exactly how each SPF mechanism (ip4, a, mx, include, exists, ptr, redirect) consumes lookups, how macro expansion works for dynamic IP-based checks, and how mechanism ordering and qualifiers interact.

Jun 13, 2026