Using Email Alerts with SMTP Relays

If you are using a email relay to send CheckPoint Email alerts, make sure to check that the server is not blocking addresses not on its domain. By default, some Microsoft products are not configured for open relay or it is turned off by default. Therefore, you may experience problems with your email server if the CheckPoint service attempts to send emails, text msgs, etc. to outside email addresses which are then blocked by the email server.

Microsoft Simple Mail Transfer Protocol (SMTP) relay is a feature that lets an SMTP client use an SMTP server to forward e-mail messages to a remote domain. As described in Request for Comments (RFC) 282, sections 2.1 and 3.7, SMTP was designed with the ability to relay e-mail messages. However, if a relay is not controlled, a malicious user might use the relay to send bulk unsolicited e-mail messages. An uncontrolled host is known as an "open relay" host. By sending these unsolicited e-mail messages to the intermediate host, the malicious user can disguise his or her identity. This may also cause excessive resource use on the relay host and prevent the relay host from sending valid e-mail messages. In particular, a malicious user who sends unsolicited e-mail messages may send a single message to many recipients without using their own bandwidth.

http://support.microsoft.com/kb/304897