Troubleshooting an Outlook Add In connection to server failure

[Je]

Hi all, I've just downloaded Fiddler for the first time to troubleshoot a problem I'm experiencing with an Outlook Add In

I support Symantec Enterprise vault - an email archiving solution - on behalf of a client base. This solution comprises a server environment hosting archives of a users emails from Exchange. The user accesses their archive via Outlook using an Add In. When a user wishes to access their email archive (held on the Enterprise Vault server) they select the Add-In, which sends an HTTP request to the EV server. This can also be achieved via a web browser using the same URL, following the format http://domain/enterprisevault/archiveexplorerui.asp

From workstations outside the clients domain, Outlook Add-In (also web browser) requests fail with a 'page cannot be displayed'
Inside the domain all works as expected
From my lab domain and other tested sources all requests work correctly

My assumption is there is something environmental on the affected [remote] workstations - an incorrectly specified LAN Connection config/reverse proxy problem that is misdirecting these requests, but I need to prove this and don't know how to do it

I installed Fiddler to try and demonstrate/see this behaviour and the second I initiated my session and began running the urls, the requests immedietely hit their target and resolved

Turn Fiddler off, and the requests fail again

I've been going though the videos and documentation but haven't been able to understand exactly how Fiddler interacts with IE (or is it Win HTTP Stack?)
Does it bypass the LAN Connection settings?

Can anyone help me understand this behaviour - why having Fiddler turned on makes everything resolve correctly while with it turned off, all fail?

Any help greatfully received

[Je]

This is what I was looking for. Bonza

Figure 1 - Fiddler Web ProxyWinINet (The Windows Internet) enables applications to interact with FTP, and HTTP protocols to access Internet resources.I am sure you are familiar with 'LAN Settings' under the 'Connections' tab of Internet (Explorer) Options:Figure 2 - 'Connections' tabThe Proxy Settings under 'LAN Settings' is your computer's proxy settings which is kind of like the UI for WinINet.Figure 3 - WinINet Proxy SettingsWhen you start up Fiddler it saves your current proxy settings and changes it so it can work as a proxy for all your http traffic:Figure 4 - WinINet Proxy Settings changes on Fiddler start upAnd of course it sets back the proxy to your original settings when you close the Fiddler or stop it. You can start and stop Fiddler capturing through File -> Capture Traffic, or using F12, or using start and stop QuickExec commands.Fiddler is a Web Proxy; so it does not really care where the traffic is coming from and where it is going to. This means that you can use Fiddler on pretty much any application or device that can talk to a proxy:Figure 5 - If you can use an HTTP Proxy you can use Fiddler

[Eric Lawrence]

The blog post at http://blogs.telerik.com/fiddler/posts/13-02-28/help!-running-fiddler-fixes-my-app- explains the most common reasons that an application might work with Fiddler running and fail when it does not.

If the clients in question were hardcoded to use a fixed proxy server that was not accessible outside the domain, Fiddler would detect that condition (and make a note of it in the Log tab) at startup.

Regards,
Eric Lawrence
Telerik