[FIXED] 503 valid rcpt command must precede data error

Are you annoyed with the error ‘503 valid RCPT command must precede data’ every time you send an email through Microsoft Outlook? We are here to help you out of this issue with some essential tips and suggestions. Read the following to know why the error occurs, and how you can avoid it. 

What Causes The ‘503 Valid RCPT Command Must Precede Data’?

Sometimes when you send an email through Outlook, instead of the confirmation of email delivery, you get an error notification. This is generally called the 503 error, and there are more reasons than one for it: 

  • You might have included an apostrophe in the email address.
  • You might have a corrupt Outlook PST file.
  • Sending emails through a VPN network.
  • Not checking if the inbox is full. 
  • Improper email client setup for SMTP authentication.

You will now learn the ways to avoid this error message in your future emails.

How To Fix The Error?

We have listed four steps for you to rectify the 503 error issue. You must be able to fix this error in any one of these ways.

Step 1: Delete Apostrophes

Removing apostrophes is the most widely used method to fix this error. While entering the name of the recipient, make sure to remove any apostrophes or any other non-alphabetic characters. 

Apostrophes are not part of the email address and will prevent its delivery. After removing apostrophes you should try again to see if your error is fixed. If not, you should check out the other steps listed hereunder.

Step 2: Turn Off VPN

VPN is used when you want to browse online, but anonymously. Due to some security features, Outlook error 503 may come up while using VPN.

Try turning off your VPN if you get this error while attempting to send an email through VPN. You can send the email again after switching off your VPN. If the issue was due to the use of the private network, it would have been solved by now. Else, look for other steps.

Step 3: Check Whether Your Mailbox Is Full

Did you check if your mailbox is full? Our inbox is flooded with so many promotional and other emails that it gets full if they are not deleted periodically. 

When the maximum limit of your mailbox is reached, any other mail will not be delivered and the 503 error crops up.

You can clear this error by visiting your ‘Account Settings’ in Outlook. The steps to do this are:

File → Account Settings → Select Menu Setting → Advanced → Uncheck the box ‘leave a copy of this message on the server.’

After you complete this, check if you are able to send the email without the error message popping up.

Step 4: Set Up SMTP Authentication

This is an effective solution for removing the Outlook error ‘503 valid RCPT command must precede data’. An incorrect email client set up for SMTP authentication may also lead to this error, so you should configure the same.

Select ‘My server requires authentication’ in Outlook. 

If you are using Outlook 2016, you should follow these steps to resolve this issue:

  • Choose your email account from the Account Settings window and click ‘Change’ and then ‘More Settings’.
  • Move to the tab ‘Outgoing Server’.
  • Check the box ‘My outgoing server (SMTP) requires authentication’. 
  • Select ‘Use the same settings as my incoming mail server’.
  • Go to the Advanced tab and select ‘Outgoing Server’. 
  • The port selected should be ‘465’. 
  • Choose the SSL option from ‘ Use the following type of encryption’. 
  • Select ‘OK’.
  • Continue with ‘Next’ and click ‘Finish’ to complete the process.

You will not encounter the error again after following this procedure.


We hope the above steps help you solve the 503 error issue. As we have mentioned, even a trivial reason, like the inclusion of an apostrophe, can keep you exasperated with the error message. So, carefully follow the suggestions mentioned above and watch your emails delivered without any trouble.

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