503 Valid RCPT Command Must Precede Data 

This error is associated with sending and receiving emails. When you are going to send an email, but suddenly notice an error ‘503 valid RCPT command must precede data’, then you need not worry. Most of the users face this error due to improper authentication from your mail server.

Due to this error, you can’t send anyone an email. But the incoming email services don’t get interrupted because of this error. To solve this error, you need to do some modifications to the Settings. Let’s see how you can get rid of this issue.

Probable Causes for 503 Valid RCPT Command Must Precede Data: 

Before you go to any solutions for any issue, you must take a look at the causes behind the issue. The exact cause helps to solve the problem more efficiently. Well, this 503 valid rcpt command must precede data issue mainly occurs for two reasons. 

If you know the right cause, then it becomes easy to eradicate the cause to get the service back again. Let’s check out what the causes are:

• There’s something wrong with the email. Please verify the email before sending the email to someone. Also, make sure that your email server needs to check your email.
• The email client is not properly set as per the SMTP Authentication.

If you have figured out the reason, then you should opt for the associated solution. If you can’t identify the reason, then follow the fixes to recover from the error.

Salient Fixes for 503 Valid RCPT Command Must Precede Data: 

Basically, the problem arises due to some errors in the settings related to the server. The email can’t be sent due to some minor mistakes, as well. We have arranged some tried and tested solutions to remove the 503 issues. Try them to check if the error resolves.

Fix 1: Avoid Apostrophes

Many users have found this hack very useful. You should remove apostrophes while adding the name of the recipient for the email. If the sender of the email has informed you that he or she can’t send an email, ask them to remove apostrophes. 

Checking for the apostrophes can really solve this unwanted issue. After removing those apostrophes, you can now check if you are able to send the email.

Fix 2: Turn Off the VPN

Check if you are using any VPN connection. A VPN connection can malfunction at any time due to some security measures. If you are struggling with the sending of an email with an activated VPN connection, then you should turn off the VPN. Now, check if the same error appears or not.

Fix 3: Check the Mailbox

Have you cleared out the mailbox recently? If not, then you should try clearing the mailbox. The  503 valid RCPT command must precede data error that might arise due to this minor issue. Try to send the email or refresh your mailbox after the process.

If you use the Outlook application to handle all your emails, then you can follow the guidelines mentioned below. This process will make sure that the copies of emails don’t stay on the server.

1. Go to the Tools option.
2. Next, opt for the Account Settings option.
3. After that, select the More Settings menu.
4. You have to unmark the checkbox next to the ‘Leave a copy of this message on the server’ option under the Advanced option.

Now, check if the issue has been resolved.

Fix 4: Apply Same Settings to All

If you are using multiple mailboxes, then this fix applies to your mailboxes. You should set the same settings for all the mailboxes you are using, currently. Also, don’t forget to enable all the associated settings for your default mailbox.

Fix 5: Pop Before SMTP

Before you send any new email to anyone, you should check for if there is any new message in your mailbox. If you are an Outlook user, then press the F9 key from the keyboard to perform the same task. 

Next, you should reboot the email service. Don’t forget to run the spam filter on the email application. It can take up to 30 minutes to complete and let it set to be able to send emails just like before. After that, you can try to send the email. 

Fix 6: Set up SMTP Authentication

This fix is the most helpful to eradicate 503 valid RCPT command must precede data. Due to incorrect authentication of SMTP, users might have to deal with this annoying problem. You can authenticate the email service through the ‘My server requires authentication’ option. 

Additionally, you can change the outgoing port to 26 from 25. The change can relieve you from the headache, instantly. Some Internet Service Providers don’t support the port 25 for email services. 

However, if you use the Outlook 2016 application, then we have an excellent solution to resolve issue 503. Stick to the guidelines below if you are facing the same issue on your Outlook 2016 account.

1. First of all, expand the Outlook 2016 application.
2. Navigate to the File menu and choose the Account Settings option. Again, select the Account settings option from the drop-down menu.
3. Opt for your particular email account from the Account Settings window. Click on the account and choose the Change option. Next, select the More Settings option.
4. You have to navigate to the tab named Outgoing Server.
5. Make sure that you mark the checkbox next to the ‘My outgoing server (SMTP) requires authentication’ option. Choose the option named ‘Use the same settings as my incoming mail server’. Next, proceed with the Advanced tab.
6. Under the Advanced tab, you have to click the Outgoing Server option. Set its port as 465. Also, choose the SSL option from the ‘Use the following type of encryption’ drop-down menu. Choose the OK button.
7. After that, proceed with the Next option from the Internet Email Settings window.

Finally, click on the Finish button when the process completes.

Final Fix: Contact your ISP

If none of the above fixes is efficient for resolving the 503 valid RCPT command must precede data issue, then this is the last fix that you can opt for. The error should have resided on the server. Ask your Internet Service Provider to look upon your issue. 

Hopefully, the guide was helpful. The error 503 valid RCPT command must precede data should have disappeared now. To avoid such errors, keep cleaning the mailbox of yours at a regular interval.