When trying to send emails using a mail client, at times it generates following error.
503 Valid RCPT command must precede DATA
Reason behind the error is emails aren’t authenticated & then sent. Email hosting providers don’t allow emails to be sent without being authenticated with username and password. Such features are enabled for security reasons.
If you face similar error, login to your mail client & access the option accounts. Edit the settings OR access Properties tab for the account which shows such error. Find for Servers tab and enable the option My server require authentication.
Click on Apply & Ok. Now, try sending emails.