Solution: Try emptying your Deleted Items or Junk folders to free up space, then restart Outlook and try sending the message again.
What does this error mean?
The 503 Valid RCPT error is a communication "handshake" failure. It occurs when your email client tries to send the content of your message before the mail server has successfully verified the recipient or your identity.
Step 1: Enable SMTP Authentication
The most common cause is that your outgoing server settings are not "signing in" before sending. In Outlook, go to File > Account Settings > Server Settings. Ensure that Outgoing mail has "My outgoing server (SMTP) requires authentication" enabled.
Step 2: Check Mail Before Sending
If your server uses "POP-before-SMTP" authentication, you must verify your identity by checking for new messages first. Click Send/Receive in your mail client, and then immediately try to send your stuck message.
Step 3. Verify Recipient Address
Ensure there are no special characters, apostrophes, or hidden spaces in the recipient's email address. Sometimes, an auto-filled contact can contain corrupted data.
- Delete the recipient from the To: field.
- Manually type the full email address.
- Attempt to send the email again.
If you continue to receive this error, please check your server settings against the table below to ensure you are connecting to the correct hardware.
Common troubleshooting steps include:
- Restarting Outlook to reset the server connection.
- Disabling VPNs which may interfere with SMTP traffic.
- Checking Antivirus settings that scan outgoing mail.
If you need further assistance with your mail client configuration, please do not hesitate to contact us.
Applicable to
All Hosted Exchange,IMAP and POP accounts with Websites Victoria