Error 503: Valid RCPT command must precede DATA

The “Error 503: Valid RCPT command must precede DATA” happens when sending email. It’s telling you that your SMTP (outgoing mail) connection was not properly authenticated by your email server.

The most common cause for this error is:

  • Your email client isn’t set up for SMTP Authentication.

Setting up SMTP Authentication

Configuring SMTP Authentication in your email client requires you to edit your email account SMTP (outgoing mail) settings. Add your email address and password to the SMTP settings and you’ll receive no more Error 503 messages.

How you set up SMTP Authentication depends on the email client you use. Here’s how to set it up in Outlook 2016:

  1. Open Outlook 2016.
  2. Open the File menu and select Account Settings –> Account Settings.SMTP Authentication in Outlook 2016
  3. In the Account Settings window, select the email account you wish to set up and click Change…SMTP Authentication in Outlook 2016
  4. In the Change Account window, click More Settings…SMTP Authentication in Outlook 2016
  5. From the More Settings window, select the Outgoing Server tab.
  6. Check My outgoing server (SMTP) requires authentication.
  7. Select Use same settings as my incoming mail server.
  8. Open the Advanced tab.
  9. In the Advanced tab, set the Outgoing server (SMTP) port to 465. In the Use the following type of encryption drop-down, select SSL.
  10. Click OK.
  11. On the Internet E-Mail Settings window, click Next.
  12. Click Finish.


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