Error when trying to send mail: "553 sorry, relaying denied from your location [] (#5.7.1)"

This error indicates that your email client is not configured to use SMTP Authentication. To protect against unauthorized access to our SMTP servers, users are required to authenticate with a valid email account.

See the following articles for information on how to configure your email client to use SMTP Authentication

Outlook Express
Outlook XP/2002/2003
Outlook 2007
Mozilla Thunderbird V.1
Mac Mail
Mac Entourage