How Do I Know If A School That Contacted Me Is legitimate?

In order to ascertain the legitimacy of  a certain school, you should check your institute with the links mentioned above to see whether they feature as Listed bodies or Recognised Bodies for the purposes of conferring degrees. Moreover, If you are still in doubt then check legal framework of how the certain course is being offered by the institute and double check that the course being offered is by a Recognised Body. Check GOV.UK

List of Institutes: