An open relay is when you have Microsoft Exchange configured to let anyone use it's SMTP service to send mail. Meaning, you don't require a login/password or screen IPs before messages are submitted to your Exchange server for delivery.
This means that any spammer could find your exchange server on the internet and use it to send out massive amount of emails.
Jogi nyilatkozat - A cikkben kifejtett nézetek egy harmadik fél által nyújtottak, és nem egyezhetnek meg a honlapunkéval