SMTP AUTH is " ..an SMTP service extension [ESMTP] whereby an SMTP client may indicate an authentication mechanism to the server, perform an authentication protocol exchange, and optionally negotiate a security layer for subsequent protocol interactions. This extension is a profile of the Simple Authentication and Security Layer [SASL]. "
This is what RFC 2554 says.
For mere mortals this means that we now have a way to authenticate smtp client before we accept mail from him. If you are an ISP this is one of the most important things on a big mail server. Without this and with a lot of roaming customers, you end up being an open relay (because of your customers needs) and sooner or later spamers will use you and you will be banned on ORBS and other spam fighting list.
With SMTP AUTH you can add a layer of security to you SMTP server. While allowing legitimate customers to send e-mail from any place (IP) in the world you are preventing spamers and unauthorised people from using you SMTP server.
Here you can find some information about clients and servers that support SMTP auth and you will be able to secure your server and use the right client in a right way.
Choose one of the links below:
If you know anything that can improve this site then mail it to smtpauth@elysium.pl