550 5.7.1 📧 Email / SMTP

550 5.7.1 Relaying denied / Message rejected as spam / Unauthenticated email not accepted

The receiving (or your outgoing) mail server refused the message — relaying isn’t allowed, the sender isn’t authenticated, or it was classified as spam/policy violation.

Seen on: SMTP

Meaning

5.7.1 is a generic “not authorised” code. On your own SMTP server it often means you tried to send without authenticating (relay denied). From external servers it means a policy/spam rejection — the text after the code explains which.

Common causes

  • Sending through SMTP without authentication (relay denied)
  • Sender domain/IP on a blocklist
  • Content flagged as spam
  • Recipient’s policy (blocked sender, internal-only group)

⚡ Quick fix

  1. Authenticate SMTP (port 587 + username/password)
  2. Check IP/domain on blocklists (MXToolbox)
  3. Read the full bounce text for the policy reason

Detailed fix by platform

Shell

  1. swaks --to user@example.com --server smtp.example.com:587 --auth LOGIN --auth-user me@example.com --tls

How to diagnose

  1. Bounce — Full rejection text
  2. Auth — SMTP authentication used?
  3. Reputation — Blocklisted?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

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