The Outlook Error 503 Valid RCPT command must precede DATA can occur when sending an email. It’s telling you that your email server did not properly authenticate your SMTP (outgoing mail) connection.
The two most common causes for this error are:
- Your email server requires you to check email first before sending an email (checking email first is one way your email provider manages the security of your email account).
- Your email client isn’t set up for SMTP Authentication.
Follow these steps to fix the Outlook Error 503 Valid RCPT command must precede DATA error on your email server. These steps will work for Outlook 2016, Outlook 2019, and Outlook 365.
Checking email before sending
When you first open your email client, it automatically checks your email first. However, if you attempt to send an email after about 30 minutes and see this message, simply check your email for new messages. You’ll then be able to send an email if this is the problem (most common with Outlook).
More often, Outlook Error 503 tells you that you need to set up SMTP Authentication in your email client.
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 won’t receive any more Outlook Error 503 Valid RCPT command must precede DATA messages.
How you set up SMTP Authentication depends on the email client you use. Here’s how to set it up in Outlook:
- Open Outlook 2016.
- Open the File menu and select Account Settings > Account Settings.
- In the Account Settings window, select the email account you wish to set up and click Change…
- In the Change Account window, click More Settings…
- From the More Settings window, select the Outgoing Server tab.
- Check My outgoing server (SMTP) requires authentication.
- Select Use same settings as my incoming mail server.
- Open the Advanced tab.
- In the Advanced tab, set the Outgoing server (SMTP) port to 465. In the Use the following type of encryption drop-down, select SSL.
- Click OK.
- On the Internet E-Mail Settings window, click Next.
- Click Finish.
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