I know there is $BUILD_STATUS and &BUILD_URL variables in Email-ext plugin. But I cant find anywhere what are all variables available to me... Where can I find them all, like duration time, date etc.?
Well, email-ext has access to all the Jenkins environment variables for jobs. Below is a list in the Jenkins documentation. Some plugins also add their own variables
Edit:
The wiki page says this about tokens: To see a list of all available email tokens and what they display, you can click the "?" (question mark) associated with the Content Token Reference at the top bottom of the email-ext section on the project configuration screen.