Have a look at the Options > Advanced > Network & Disk Space > Settings... section. The dialog is almost similar to the one in Firefox, so if you configured Firefox properly for a proxy, you can use these settings. See here for more info on proxy settings in Firefox.

Make sure to only select Use this proxy server for all protocols when needed. Some proxies do not support all protocols, so chances are not everything will work as expected when you do. You system administrator or ISP should be able to tell you what settings are required.

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There ought to have a step by step guide to configure the proxy setting in Thunderbird. I am groping in the dark. What is to be given where, no idea. I am looking for a lead to begin. Please help

There is not much to tell about what to enter in Thunderbird’s (or Firefox’s) proxy settings. The dialog is not much different from the one for Internet Settings in Windows or any other program. If your ISP or corporate network requires you to use a proxy, they are the one to provide the settings (a server name and port) - this is not a task for Thunderbird or anyone else, as they simply don’t know your network requirements. Please contact your ISP or network administrator and they will be happy to provide the info.

On the other hand, you wrote "I used to work with Thunderbird smoothly until the internet connection was made to a proxy server".

What was "made" to use a proxy server? Or did you mean the Thunderbird connection settings (suddenly) changed so they were set up to use one without fields being entered, or they changed to "Use system proxy settings" with no reason and Thunderbird started failing? In that case, just select "No proxy" and it should be back to normal.

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