Sending email through Microsoft Outlook returns a bounce message containing the following reason: "503 valid RCPT command must precede DATA"
Solution
This error means that you will need to enable SMTP Authentication in your email client. When your Desktop email client attempts to send an email from our server it must authenticate. The Username and Password you would use would be the same as your incoming username and password.
Kindly use the below settings to configure the E-mail client for the account.