SPF (Sender Policy Framework)

SPF, or Sender Policy Framework, is an email authentication standard that lets the owner of a domain declare exactly which mail servers are permitted to send email using that domain. It is published as a single TXT record in the domain DNS. When a receiving server gets a message, it checks whether the sending server appears on that authorized list.

Why it matters for outbound

SPF is one of the three pillars (alongside DKIM and DMARC) that mailbox providers use to decide whether to trust a sender. Without a correct SPF record, cold email is far more likely to be filtered to spam or rejected outright, because the message looks like it could be forged. For outbound at scale, a misconfigured SPF record can silently suppress an entire campaign.

Getting authentication right is foundational, which is why Outword verifies it before any sending begins.

How it works

• The domain owner publishes an SPF record listing approved sending sources.
• A receiving server reads the record and compares it to the sender of the incoming message.
• A pass strengthens trust; a fail or soft fail weakens it and may route the message to spam.

A common pitfall is the ten DNS lookup limit: chaining too many included sources causes SPF to fail with a permerror. SPF only checks the envelope sender, which is why it is paired with DKIM and DMARC for full coverage. See our deliverability service for how the full stack is configured.