If any one wants to send emails from an external email client like Kmail, Evolution, Ourlook express etc, he need not provide authentication details if he pop’s emails from his account before sending emails. If you’ve already read mails from the server, the servers lets you send emails at the same time by allowing relay for your IP (Global ip which will be allocated by your ISP when you connect to internet. To find the global ip use “What is My IP“.
Pop-Before-SMTP feature allow the email account which gets authenticated to pop emails by adding the users IP to relay hosts list for some time. Most of the administrators have it on in their servers as some lazy users don’t like to provide authentication details once again for sending emails. This could turn out to be an issue when there is a worm, spyware or virus on your users computers. The virus or spyware can utilizing open relay to send spam from the servers.
I was just trying to remove this feature from Qmail server and here is the step used to disable it. You need to read the documentation or wiki for other email servers to achieve the same result.
You can disable POP before SMTP by uncommenting “disable_external_relay” in ~vpopmail/etc/vlimits.default.
Have you disabled this on any other email server? Share it with me.