Proxy Error: "The proxy server received an invalid response from an upstream server." When Accessing Webmail

Overview

When accessing Webmail, you might get the following Proxy Error message.

502: Proxy Error
502 Proxy Error
PROXY ERROR
The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request POST /webmail/api/jsonrpc/.
Reason: Error reading from remote server


 

This article provides information on how to resolve this issue. 

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Prerequisites

You should configure Apache Reverse Proxy Server in front of Kerio Connect.

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Process

1. Log in to your Kerio Connect server and stop Kerio Connect service.
2. Navigate to Kerio Connect installation folder.
   
   Default folders are as follows:

   • Windows: C:\Program Files\Kerio\MailServer
   • macOS: /usr/local/kerio/mailserver
   • Linux: /opt/kerio/mailserver
3. Open the mailserver.cfg file, and modify the LongPollTimeout variable under <table name="Webmail">, as shown below.
   
   <variablename="LongPollTimeout">30</variable>
    
   
    
   
   Note: The default value is 600.
4. Save the changes.
5. Start Kerio Connect.

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Confirmation

Webmail can be accessed without receiving the Proxy Error message.

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Supplemental Information

The LongPollTimeout variable indicates the timeout period in seconds, which is used for requests utilizing the Long Polling technique. Webmail client needs to instantly get updates about emails, calendar actions, etc., without page reload. Thus, Long Polling technique is used to ensure that.

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Useful Resources

Nginx in front of Kerio Connect

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