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The beautiful soup library of python is useful in building web scrapers, we can make scrapers if all the websites are figured out. https://www.crummy.com/software/BeautifulSoup/bs4/doc/
Using Beautiful Soup library is good if one have necessary coding skills and thus build a crawler out of it. But, if the goal is only to extract email ids and its verification, then https://snov.io/ will be at better place.