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On Tue, Sep 22, 2015 at 04:22:11PM +0100, Matt Stevenson wrote: > Is there a full proof way of checking if its definitely an open relay, if it is > how do I shut it down? An open relay mail server accepts email for anyone from anyone and relays it to the correct recepient. If the mail server is an inbound one (it receives email from the Internet for your users), set it so that it accepts only emails for your domain(s). If the mail server is an outbound one (it receives emails from your users and relays them to the Internet) make sure it only accepts mail from certain IP ranges and/or certain authenticated users. I'm not sure how to do this in Exim though. Given that only Symantec has discovered you're running an open relay, it may be a bit more subtle than this though. A true open relay would have been discovered by spammers which at least would have led to further blacklisting. My guess is that it's merely accepting email for all domains, but doesn't relay those emails. That's not bad, but something you'll want to fix if you also send emails from the same IP address - which you do. You can use telnet to check if it does accept emails for other domains. Martijn.
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