Zimbra Forums

HTTP ERROR 502
Problem accessing ZCS upstream server. Cannot connect to the ZCS upstream server. Connection is refused.
Possible reasons:
upstream server is unreachable
upstream server is currently being upgraded
upstream server is down
Please contact your ZCS administrator to fix the problem.

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It has been like this almost a year.
Would like to be able to use it again.

You've posted this in the Zimbra Desktop forums, is that the product that's in use? If it's ZCS that you're using you need to (always) give the version that in use by posting the full output of the following command:
As you've mentioned that this problem has existed for 'almost a year', what stpes have you taken to research the problem and have you searched the forum for any similar threads on the topic.

Without any helpful information from you it's not easy to determine what the problem is.