Not an easy bug to track down, but I think I've rooted out the cause
of your problem, along with a potential solution.
It appears to be a bug which only occurs in Internet Explorer 6, with
Service Pack 1 (that is, the latest version from Microsoft). The file
wininet.dll contains a bug, which means that the GET request is sent
in the same session as the proxy authentication. This means that the
first webpage (or email) which is requested, after proxy
authentication, will be denied.
You can see an acknowledgement of this problem here:
And a good description here:
The fix is surprisingly simple - just use the older version of
wininet.dll which came with Internet Explorer 6 (no service pack).
Here's a full description of the method used to do this:
You can find the old version of wininet.dll on your original Windows
CD (the location varies depending on the version). Or, you can attempt
to download it from the web: this site appears to offer the correct
Be aware that in Windows 2000 and Windows XP, you will have System
File Protection enabled, which may make it difficult for you to change
wininet.dll. See this page on how to disable System File Protection
(though I'd recommend you re-enable it after changing the DLL
Once the older version of wininet.dll is in place, this problem should
disappear. And hopefully, Microsoft will fix this problem in the next
IE6 service pack.
I hope this answers your question! If anything's unclear, or any of
the links do not operate, then please don't hesitate to request
clarification before rating this answer.
All the best,
Search strategy (on Google and Google Groups):
IE6 proxy problem
IE6 refresh proxy problem
IE6 SP1 squid problem