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IO Exception: Unable to tunnel through proxy. Proxy returns "HTTP/1.0 503 Service Unavailable

I get this exception, intermittently, when performing an async ws callout.  Some days everything is fine.  The endpoint is behind a ton of network security appliances (local dmz).


Does this exception denote a problem with the SF or local environment?  I am thinking local since there is so much hardware to traverse before hitting the true endpoint...but, how can I be sure?  Of course, the local guys are pointing fingers to SF infrastructure;)



Trust your instincts.  This is a local environment problem with your firewall/proxies.

Hi Bob,


I'm encountering this same problem from last few days. I have imported a WSDL and doing a future call from class. Its was working fine when I built this few weeks earlier but then had a small gap before moving to production. But now when I thought of moving to production I's seeing this error. No clue what so ever or what direction showed be taken from here. Were you able to get to cause of it, what did you do to get this resolved ? greatly appreciate any advise


Updating so this would help others with any similar issues. The issue was from the WSDL provider with firewall & proxy provider. They fixed and its all going smooth now.


Can you share what changes did the WSDL provider make to fix this?




I have the same problems with my Webservice.


Can you share your usue plz ?






What we found out is that this is a firewall issue where your web service is hosted.  When a request to the web service is made from Salesforce, it expects the response returned by the web service to come from the same IP address as when the request was made.  In our case, our IT had configured the firewall so that incoming request was going through one IP address, but outgoing response was going through another IP address.  Definitely check with your IT to figure out a solution.  One possibility is to put the server hosting the web service outside of the firewall.


Hope that helps.  Good luck!


Thank you very much Alin !!