DotNetOpenMail.EmailMessage email = new DotNetOpenMail.EmailMessage();
            
            email.FromAddress = new DotNetOpenMail.EmailAddress("zhifengwu1211@126.com");
            
            DotNetOpenMail.EmailAddressCollection toAddresses = new DotNetOpenMail.EmailAddressCollection();
            DotNetOpenMail.EmailAddress toAddress = new DotNetOpenMail.EmailAddress("zhifengwu1211@126.com");
            toAddresses.Add(toAddress);
            email.ToAddresses.Add(toAddress);

            email.Subject = "this is test";
            DotNetOpenMail.SmtpServer smtpserver = new DotNetOpenMail.SmtpServer("192.168.2.129");
            
            StreamReader readfile = new StreamReader("d:\\mycert.cer");
            Byte[] fileBytes = System.Text.Encoding.Default.GetBytes(readfile.ReadToEnd());
            
            DotNetOpenMail.FileAttachment fileAttachment = new DotNetOpenMail.FileAttachment(fileBytes);
            fileAttachment.FileName = "mycert.cer";
            email.AddMixedAttachment(fileAttachment);
            

            bool result=email.Send(smtpserver);
           
            if (result == true)
                this.label1.Text = "success";
            else
                this.label1.Text = "error";