No, IELTS is not necessary for every universities abroad
But, you would have to take either IELTS or TOEFL based on your study destination/university. IELTS is jointly administered by University of Cambridge Local Examination Syndicate (UCLES), British Council and IDP Education Australia. And TOEFL is administered by US-based organisation. So, if you are looking for UK or any other Common Wealth countries, I would say, go for IELTS. If USA is what you have in mind, go for TOEFL. Hey, also do checkout the university requirements :)