How to write a code to check an email is existing or not? For example donkey_sdh123@gmail.com, donkey_sdh123@yahoo.com, or donkey_sdh123@lycos.com all these emails do not exist in gmail, yahoo and lycos database.

See the screenshot. donkey_sdh123@gmail.com is bad. That means it does not exist. how can i implement the same thing in my project?
javascript, jquery shell script, c or c++ are welcome. Without .net.
See this code i got it from web.