Why do I get a "Relaying Denied: Authenticate with POP first" error when trying to send email?

You're trying to send email and are getting an error, "Relaying Denied: Authenticate with POP first," or similar.

You need to login to 'receive' or 'check' your mail first!

The server has an anti-spam feature that prevents anyone from using the smtp server until they have logged in first. This keeps just anyone from connecting to the server and sending out thousands of messages. Once you have logged into the pop server and have been authenticated, you will be allowed to send mail.