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I run technology for an international non-profit, so I have users that could be checking their email from Pennsylvania one day, Santo Domingo the next, and Kabul, Afghanistan, the next week. Recently, I'm seeing a strange behavior - where it appears that their spam filtering (logically on their client - Entourage or Outlook) behaves differently when accessing the email overseas. Does that make any sense at all? Does anyone have any experience like that?

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More info needed. What spam-filtering software? What message infrastructure are you running? What's the change in behavior? Which countries are you based in, and travelling to? – Chris Thorpe Jul 16 '10 at 0:51
Define "differently". – Dennis Williamson Jul 16 '10 at 2:32

No, it shouldn't be doing anything differently depending on where the client is physically located. The only reason that they might act differently would be if they weren't able to get updates from the servers while there which would then let the SPAM come in.

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There may be a remote chance that some of the foreign ISP access is running through transparent proxies which may not be that "transparent" where the proxies may be leaving their SMTP header entries in the actual message delivery transaction. Those headers may reflect IP ranges (of the ISPs/their proxies) which have been identified as "problematic" depending on how the spam weighing/computation is derived.

The first point of troubleshooting this further may be to examine the message headers of those mis-classified messages carefully.

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