Outlook Error: 503 valid RCPT command must precede DATA

The error “503 valid RCPT command must precede DATA” typically occurs when the email client (like Outlook) tries to send an email without specifying the recipient properly before sending the message data. This is usually a SMTP configuration issue.

Common Causes and Fixes:

1. Authentication Not Enabled for Outgoing Mail

• Most common cause.

• Outlook needs to authenticate with the SMTP server before sending mail.

Fix in Outlook:

1. Go to File > Account Settings > Account Settings.

2. Select your email account and click Change.

3. Click More Settings > Outgoing Server tab.

4. Check the box that says:

   “My outgoing server (SMTP) requires authentication”

5. Select:

   “Use same settings as my incoming mail server”

2. Incorrect SMTP Port or Encryption

Make sure you’re using the correct SMTP port and encryption:

Check under:

• More Settings > Advanced tab

  • Outgoing server (SMTP): use 465 (SSL) or 587 (STARTTLS)

  • Make sure encryption type matches the port.

3. Sending Without a Recipient

If the message has no recipient or malformed headers, the server can’t process it properly.

Fix: Make sure:

• You have a valid “To” address filled in.

• No stray characters or corrupted email headers.

4. Antivirus/Firewall Interference

Security software (e.g., Avast, Norton) may intercept or modify SMTP traffic.

Fix:

• Temporarily disable your antivirus/firewall and test.

• If this resolves it, configure your AV to exclude email scanning or switch to a different security solution.

5. SMTP Server Settings in cPanel

Double-check that the mail domain and user are configured correctly in cPanel:

• Valid MX records.

• Email account exists.

• SMTP limits are not exceeded.

If you’ve checked all of the above and the error persists, please reach out to us and let us know:

• Whether you’re using IMAP or POP3,

• Your SMTP server name (e.g., mail.yourdomain.com),

• The port and encryption settings used,

• And the full error message if available.