Root Causes of Outlook 503 Error Valid RCPT command must precede DATA
Usually, when you get the Outlook 503 error message while trying to send emails, it can be due to any of these two main reasons listed below:
You must first confirm the email before sending an email (verifying the email first is one of the ways email providers can use to protect your email account). If you did not verify the email before sending it, you may receive the Error 503 Outlook message.
The most common reason for this message is incorrect or incorrect email client settings for SMTP authentication.
These two are the causes of the Outlook 503 error. Valid RCPT commands must precede the data. Let us now discuss how to fix this error.
How do I fix the Outlook 503 error? Must the valid RCPT command precede the DATA?
Usually, the Outlook error 503 issue arises as a result of some errors in the settings connected to the email server. Email cannot be sent due to some trivial errors as well. Here are some organized solutions that have been tested to eliminate and fix Outlook 503 error issues;
1. Remove apostrophes
Most of the users who had the Outlook 503 error found it very useful. When entering the name of the email recipient, be sure to remove the apostrophes. Also, if the sender of the email tells you that they can't seem to send an email, ask them to remove any apostrophes present.
Confirming if apostrophes are used can resolve this unwanted issue. After removing the apostrophes, you can continue to confirm if you can send the email.
2. Turn off your VPN
VPN connections help you stay anonymous online. If you are using any and encounter Outlook error 503, make sure to turn off the VPN connection because a VPN connection can malfunction at any time as a result of some security measures. After turning off your VPN, try sending an email again or confirm if you still get the 503 error message.
3. Check your mailbox
Is your mailbox full? If so, you need to have it removed immediately. The valid 503 RCPT command should precede a data error which can also arise due to this seemingly minor issue.
Using Outlook to send an Email, Confirm that copies of emails are not saved on the server;
Clicking on the file option
By clicking on the account settings option
Clicking on the setup option from the select menu
Clear the checkbox next to the advanced option next to leave a copy of this message on the server.
After following these processes listed above, try to resend the email or refresh your mailbox after emptying it to confirm if the 503 error Outlook issue still occurs.
4. Confirm before SMTP
Before you try to send a new email to someone, it's important to confirm if there are any new messages in your mailbox. With Outlook, press the F9 key on your keyboard to perform the same task.
After that you have to restart the email service. Remember to run the spam filter in the email app, which can take up to 30 minutes to complete and allow it to restart so you can send emails like before. After this you can try to send the email.
5. Configure SMTP authentication
This is the most useful solution to completely remove 503 valid RCPT commands that must precede DATA. As a result of incorrect SMTP authentication, many users have been dealing with this issue. To authenticate the email service, simply navigate to the 'Server requires authentication' option.
Also, you can decide to change the output port from 25 to 26. This quick change can instantly relieve you of the hassle. Unfortunately, some service providers may not support port 25 for email services.
However, if you are using the Outlook 2016 application, this is a great solution to resolve the 503 issue. The valid RCPT command must precede the DATA. To set up your SMTP and resolve 503 issues, please follow the steps listed below;
Click on your particular email account as shown in the Account Settings window, then click on the account and choose the 'Change' option. Next, choose the More Settings option.
Next, navigate to the tab named Outgoing Server.