Error: Specified string is not in the form required for an e-mail address

This error may occur when you are working with .net 1.1 means when using the namespace Sytstem.Web.Mail. If we want to send email to multiple or more than one person usually we use like:

To=aaaaaaa@gmail.com;bbbbbbbb@gmail.com;ccccccccc@gmail.com;

This will work in the namespace Sytstem.Web.Mail because here we use semicolon to split or separate email ID's.

But the ERROR: "Specified string is