When sending an email from Outlook, the “Error 503 Valid RCPT command must precede DATA” error may appear. It is to inform you that your SMTP (outgoing mail) connection’s authentication by your email server is not working.
How to Set up SMTP Authentication
You need to tweak your email account’s SMTP (outgoing mail) settings in order to configure SMTP authentication in your email client. You won’t see any more “Outlook Error 503 Valid RCPT command must precede DATA” errors if you add your email and password to the SMTP settings.
Follow the instructions given below to solve the error Error 503 Valid RCPT command must precede DATA:
1. Open Outlook 2016.
2. Open the File menu and select Account Settings > Account Settings.
3. In the Account Settings window, select the email account you wish to set up and click Change…
4. In the Change Account window, click More Settings…
5. From the More Settings window, select the Outgoing Server tab.
6. Check My outgoing server (SMTP) requires authentication.
7. Select Use the same settings as my incoming mail server.
8. Click on the next Advanced tab in the same dialog box.
9. In the Advanced tab, set the Outgoing server (SMTP) port to 465 (Sometimes default also works but you need to change the type of encryption. In the Use, the following type of encryption drop-down, select SSL or Auto.
10. Click OK.
11. On the Internet E-Mail Settings window, click Next. Once you click on Next it will automatically verify the setting by sending an email.
12. Once done, click Finish.
