ERROR: "550 No such user here" when sending mail

When attempting to send an email, your email client may report one of the following error messages:

• 550 No such user here
• 503 This mail server requires authentication when attempting to send to a non-local e-mail address. Please check your mail client settings or contact your administrator to verify that the domain or address is defined for this server.
• 503 This mail server requires authentication. Please check your mail client settings.

Although receiving mail works correctly.

This error message is reported by the e-mail server to your email client such as Outlook because the check box labeled "My Server Requires Authentication" is not checked.  Your email client attempts to send the email to the server without providing a password, hence the server replies that you are not allowed to relay without proper authentication.

Resolution:To resolve this issue check the check box next to "My Server Requires Authentication".

> Open Outlook 2003/2007
> Click Tools
> E-Mail Accounts > View or change existing e-mail accounts
> Select the email account
> Click Change
> Click 'More Settings'
> Click the 'Outgoing Server' Tab
> Check the checkbox "My outgoing server (SMTP) requires authentication"
> Click OK
> Next
> Finish