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A company that we deal with has their internal network numbered with, specifically a mail server. That IP range belongs in China, causing all of their mail to be flagged as suspicious by our SPAM filter.

I found this rant about using other people's IP's on your network:

Do you know of any better articles/rants about this subject? This one is not convincing enough for me.

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If they aren't convinced of the stupidity of their ways by their email being classified as Chinese spam, I don't think any article or rant is going to do a better job at convincing them. – HopelessN00b Jun 27 '12 at 13:26
This type of behavior is very common, even among large hardware vendors who should know better. As an example, Compellent (now owned by by Dell) uses a DoD netblock for the heartbeat circuit between SAN head units. I tried to get someone in their support org to see that this is a bad thing to do, but no one seemed to understand the problem. – EEAA Jun 27 '12 at 13:39
For some organisations this can be a historical issue. IP networks were growing in popularity before businesses thought they'd be exposing internal systems to the Internet. There may well be a lot of reasons why it's non-trivial to reverse old decisions, and it comes down to business cost. – EightBitTony Jun 27 '12 at 13:58
up vote 3 down vote accepted

You already have a reason to present to them - the incorrect spam flagging.

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The reply will likely be: "Oh, can't you whitelist that range?" since it's easier to impose costly time and effort on someone else than fix the problem correctly. – cjc Jun 27 '12 at 14:00
Then you say "No, because those IPs aren't unique, because you're breaking the Internet, you jackass." Suitably edited for business purposes, of course. – mfinni Jun 27 '12 at 15:51

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