Postigo
Войти Попробовать бесплатно
503

Bad Sequence of Commands

SMTP commands were sent in the wrong order, often indicating missing authentication.

What does this error mean?

SMTP error 503 means commands were sent out of order or a required step was skipped:

  • Authentication required before sending
  • HELO/EHLO not sent before MAIL FROM
  • MAIL FROM not sent before RCPT TO
  • Protocol steps performed out of sequence

Common Causes

  • key
    Authentication Missing

    The server requires authentication (AUTH) before accepting mail commands.

  • format_list_numbered
    Wrong Command Order

    SMTP commands were sent in an incorrect sequence.

  • restart_alt
    Session Reset

    The session was reset unexpectedly, requiring commands to start over.

    • How to Fix

    1. Enable Authentication

    Configure your mail client or server to authenticate (SMTP AUTH) before sending mail.

    2. Check SMTP Settings

    Verify that your outgoing mail server settings include proper authentication credentials.

    3. Update Mail Software

    Ensure your email client or server software is up to date and properly configured.

    Example response 
    503 5.5.1 Error: authentication required
503 Bad sequence of commands
503 5.5.1 RCPT first

    Related SMTP Errors

    530 Authentication Required 500 Syntax Error 502 Command Not Implemented 504 Parameter Not Implemented

    Tired of SMTP errors?

    Postigo автоматически обрабатывает ошибки и ротирует SMTP-аккаунты для максимальной доставляемости.

    Попробовать бесплатно