Error while sending mails : 503 Valid RCPT TO must preced DATA

Like following :
"'task stewarth@stewarthome.com- Sending' reported error (0x800CCC65) :'Your outgoing (SMTP) mail server has reported an internal error. If you continue to receive this message, contact your server administrator or Internet service provider (ISP). The server responded: 503 Valid RCPT TO must preced DATA'.
Solution :
First try checking "My Server Requires Authentication" else Need to delete his email account and recreate it again and that will fix the problem.
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The server responded: 503 valid RCPT command must precede DATA means you must check your email before trying to send mail. The mail server requires authentication, which can be achieved using one of these methods:
1. Pop before smtp -- check your email for new mail before trying to send email. This adds your IP address to a relayhosts file and allows any email to be sent from that IP address for up to 30 minutes. After 30 minutes you have to authenticate again.
2. Configure your email client to authenticate automatically by checking the "my server requires authentication" box in your email configuration. You will be able to send mail without having to "pop" your mail box first.
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503 Valid RCPT
Sometimes an email does not get sent out if they person who is recieving the email is blocking the specific email address. That usually means they need to log in to the POP server.
503 mail server is not resolving with our ip address if you are on a newer server you might want to check with your isp to make sure that the ip address is resolved.