iPhone 5s is creating "contacts" from multiple addressees of e-mails...why?

iPhone 5s is creating "contacts" from multiple addressees of e-mails...why? NEW company phone synched to receive company e-mails (outlook). I am finding that my contact list is being populated with contact entries representative of multiple addressees on e-mails I have received. I did not create these. What is causing this, and how do I alter the setting? THANKS!!!