How to Add data to Dropdown in windows forms applications in C#

I am trying to create a windows form application. To create a .Zip file with a password and sending the .zip file to the clients email address in one email and another email to send password of the .zip file to the client...

I am using a dropdown box to enter "TO:" email address... and I want the user not to write the entire email address if it is an frequently used email ID.. So want the whole email ID to display if entered starting part of it... (Like an intellisense) and if it is a new one then make a new entry.. I am not sure how to implement this.. as looks like dropdown does not do this..

Any one please help me or suggest how to achieve this functionality..

Thanks in Advance!