Hi fredarator,

 It seems like that the class EmailHelper is in the namespace Comm.  In order to use the method SendMailMessage in the code behind, you can add the namespace and modify the code as follows:

protected void Button1_Click1(object sender, EventArgs e)
        {
            Comm.EmailHelper comm = new Comm.EmailHelper();
            comm.SendMailMessage(txtEmail.Text, txtNotes);
        }

Or add the namespace in the code behind as follows:

using Comm;

In addition, you need to delete the static for your method.

You can also follow aamirha's advice to call the method directly.

Best wishes,