Email Error 503 Valid RCPT command must precede DATA

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In this Article

  • Cause for the 503 Valid RCPT command must precede DATA error.
  • Solution 1 – Validate email.
  • Solution 2 – No cPanel mailbox account disk space available.

Error: 503 Valid RCPT command must precede DATA

Your message did not reach some or all of it’s intended reciptients.

Subject: XXXXXX

The following receipient(s) cannot be reached:

‘Joe Blogs’ on DAY-MONTH-YEAR

503 Valid RCPT command must precede DATA


  1. This error is usually received as an immediate bounced email when trying to send an email due to SMTP authentication disabled.
  2. In some circumstances, when using cPanel as your hosting control panel a lack of mailbox disk space causes this error.


1) Authenticate SMTP (email sending)

You must authenticate your mail email before trying to send. And in the case of Web Assist’s mail servers as with most other hosting companies those credentials are usually the same as the incoming credentials.

To automatically do this, ensure that you check the “my server requires authentication” box in your email client and it will use the same sending credentials that it uses for receiving email.

If you’re using Microsoft Outlook then do the following:

  1. Go to Account Settings
  2. Click on Email
  3. Select the Mailbox in question > Change
  4. Click More Settings…
  5. Click Outgoing Server
  6. Check the My Outgoing Server (SMTP) Requires Authentication box
  7. Click the Use sames settings as my incoming mail server radio button to automatically do this
  8. You can click OK and continue as this should fix the error but if not
  9. In the same More Settings… area, click the Advanced tab
  10. Change the Outgoing server (SMTP) port from 25 to 587
  11. Click Ok and test your account settings again

2) Increase Mailbox Disk Space in cPanel

  1. Login to cPanel.
  2. Check your mailbox settings in cPanel to check your mailbox disk quota.
  3. If your mailbox has ran out of disk space i.e. has no available disk space:
  4. Edit the mailbox to increase the disk quota.

If you are still having difficulty please contact Web Assist Support and we’ll gladly assist.

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