When you try to send an e-mail message by using the System.Web.Mail namespace in the Microsoft .NET Framework 1.0, you receive the following error message:
0x80040220 - The 'SendUsing' configuration value is invalid
This issue occurs after you try to use the String.Insert method to change the SmtpMail.SmtpServer property. For example, the issue occurs when you try to send an e-mail message after you use code that resembles the following:
SmtpMail.SmtpServer.Insert(0, "mail.mycompany.com");