title: Checking a valid company or university email address
body: <p>I want to check a email address whatever it is a company email address like from some company(xyz@stackoverflow.com) or educational institute etc or not. for example I can refer "Yammer" site. They are not taking general email address like yahoo or gmail or any other public email address for registration. I can only register with my university email address not others. How do they check this. I want to do similar things with PHP.</p>
  
  <p>Any Idea or suggestion will be very helpful for me.</p>
  
  <p>Thanks in advance</p>