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Open Relay

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Email Open Relay


Within your anti-spam security solution, you can configure internal hosts your anti-spam firewall will relay email for to the outside world. You would also configure the domains you would accept email to from the outside world.

However, if these settings are left untouched, you would be leaving your server open, which is known as an open relay, which poses a major threat in which anyone can use the open relay server to send email messages inbound or outbound using the resources of that server. In this scenario, a spammer would able send large volumes of email messages through the server, due to the relay settings being un-configured and unrestricted for anyone to use, meaning the relay server would accept email from anyone and destined to anyone. In this situation you would very quickly find your domains and IP addresses blacklisted, and your server processing an unprecedented amount of email messages.

Further Reading

Wikipedia's guide to Open Relay