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This puzzled me. We have all mail directed to an ISP's spam filter, then delivered to SBS 2008 Exchange. One of the ISP's IP numbers suddenly appeared in the ES2007 block list, set to expire in 24 hours I think, so emails started bouncing.

Quick look through the typically ponderous docs, and I can't see anything that says Exchange will auto-block an IP number, but nobody is admitting to adding it manually and I think it must have done.

Anyone know about this or where it is configured? Obviously one could disable block lists completely but I'd like to know exactly why this happened.

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are you using blacklists, SBL etc? – Sam Mar 1 '10 at 15:28
No, everything is left at the SBS 2008 default. Tim – Tim Anderson Mar 4 '10 at 17:02

You need to put the ip address of your router in the IP Allow list. Use the Hub Transport under SERVER CONFIGURATION, not Organization Configuration. Double click it, select the Allowed Addresses and Add your router IP address to the list.

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I don't have an answer for you, but this week the exact same thing happened to me. I have my SBS server behind a router/firewall where its services are portmapped. The IP address of my SBS server is, The IP of the router is Monday morning everyone was complaining that noone was getting outside mail. I looked in the blocklist, and the ip address for the router (250) was in it, with a 24 hour expiration starting 6:30am that morning. Noone could/would have added it, I certainly didnt, and looking at my firewall logs it's unlikely an outside force. (in fact, why put the expiration at all if it is a virus)
I'm posting this hoping that someone will come accross it and look for an answer, I havent slept soundly since Monday ;-)

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We thought it might me the "sender reputation" option in anti-spam. We also added the IP no. to the whitelist IIRC. Tim – Tim Anderson May 7 '10 at 16:31

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