You can try this:
Step1 (code):
SmtpMail.SmtpServer = "mail.company.com";
SmtpMail.Send(from, to, subject, body);
Step2(config SMTP):
IIS => Default SMTP Server Mail go to Properties (right click) and on tab "Access" you'll find "Authentication" (you have to test the possibles configurations and to find the right one).
Hope this help.