550 5.7.23 Error: SPF validation failed — Causes & Fix | InboxVerify
SMTP error code

550 5.7.23 — SPF validation failed

Updated October 12, 2026 · By the InboxVerify team

The sending IP is not authorized by the SPF record of the envelope sender domain, and the receiver refused the message.

Policy rejection · fixable

Common causes

  • The service or server you send from is not in your SPF record
  • Your SPF record ends in -all and a forwarder relayed the message
  • Two SPF records exist, which makes SPF invalid

How to fix it

  1. Use the SPF Checker with your sending IP to see what is missing
  2. Add the right include: or ip4: mechanism and keep a single SPF record
  3. Stay under the 10 DNS lookup limit
SPF CheckerRun the right check for your domain or paste the full bounce message for a precise explanation.
Open SPF Checker →

Frequently asked questions

What is the difference between 5.7.23 and 5.7.26?

5.7.23 is specifically an SPF failure. 5.7.26 means several authentication checks failed (typically DMARC). A broken SPF record (PermError, e.g. more than 10 lookups) is reported as 5.7.24 "SPF validation error".