Home/Transactional Email/SPF Email Authentication

SPF Email Authentication: How It Works and the Lookup Limit

By Kam Low ยท Updated 2026-07-27

SPF Email Authentication

SPF (Sender Policy Framework) is a DNS record that lists which servers are allowed to send email for your domain, so receivers can reject mail from unauthorised sources.

How SPF works

You publish a TXT record naming the IPs and services allowed to send as your domain. When a server receives mail claiming to be from you, it checks the sending IP against that list. If the IP isn't authorised, SPF fails, and combined with DMARC that mail can be quarantined or rejected.

The ten-lookup limit

SPF allows a maximum of ten DNS lookups per record, and each included service (your ESP, your CRM, your helpdesk) can consume one or more. Exceed ten and SPF fails with a permerror, silently breaking authentication. Flattening or consolidating includes is the usual fix.

SPF is necessary but not sufficient

SPF alone doesn't stop spoofing of your visible from address, which is why it pairs with authentication's DKIM and DMARC. Alignment between the SPF domain and the visible from domain is what DMARC actually checks.

How Nitrosend handles SPF

Nitrosend provisions the necessary records automatically and the compliance layer flags SPF problems, including the lookup-limit trap, against the 2026 bulk-sender requirements.

FAQ

What is SPF email authentication?

A DNS record listing which servers may send email for your domain, so receivers can reject mail from unauthorised sources.

What is the SPF ten-lookup limit?

SPF allows at most ten DNS lookups per record. Exceeding it causes a permerror that silently breaks authentication, usually fixed by consolidating included services.

Nitrosend is the fastest email platform that works where you work. Prompt it from Claude. Trigger it from your code. Let it automate email marketing across the brands, products, and clients you manage in Codex.

It's full stack email automation inside your AI agent, not an email marketing tool with AI added.

We're obsessed with speed. Not because speed is trendy, but because speed is the thing that separates the people who ship things that change lives from the people who plan to ship. Every minute you spend configuring email automations is a minute you're not talking to customers, writing code, or selling.

We believe the best tools disappear into your workflow. You shouldn't have to learn our interface.

We're George, Ed and Kam, and we're building Nitrosend because the world has shifted and email hasn't caught up. Until now - welcome to faster email.