550-5.7.26: Sender is unauthenticated

GmailSMTP

The error usually looks like this:

550-5.7.26 Your email has been blocked because the sender is unauthenticated. Gmail requires all senders to authenticate with either SPF or DKIM.

What it means

Gmail rejected the message because it passed neither SPF nor DKIM – or failed the sending domain’s DMARC policy.

Common causes

  • Your domain has no SPF record, or the record doesn’t include the server that sent the message.
  • DKIM signing isn’t set up for your domain with your email service.
  • Your domain’s DMARC policy is quarantine or reject, and the message failed DMARC.

How to fix it

  1. Check your SPF, DKIM and DMARC records, and add any missing sending services to your SPF record.
  2. Enable DKIM signing with every service that sends email for your domain.

Tools to help diagnose it

SPF, DKIM, and DMARC checker

Check your domain’s email authentication DNS records, count SPF lookups and diagnose deliverability issues

SPF record generator

Build a valid SPF record for your domain from the email services you use

DMARC record generator

Create a DMARC policy record with reporting, step by step

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Read the docsTry Auth-Email →

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