c# - Error in sending email with a button -

what want send email through button click attached image it. have code aspx page:

<div> <table style=" border:1px solid" align="center"> <tr> <td colspan="2" align="center"> <b>send mail using gmail credentials in asp.net</b> </td> </tr> <tr> <td> gmail username: </td> <td> <asp:textbox id="txtusername" runat="server"></asp:textbox> </td> </tr> <tr> <td> gmail password: </td> <td> <asp:textbox id="txtpwd" runat="server" textmode="password"></asp:textbox> </td> </tr> <tr> <td> subject: </td> <td> <asp:textbox id="txtsubject" runat="server"></asp:textbox> </td> </tr> <tr> <td> to: </td> <td> <asp:textbox id="txtto" runat="server"></asp:textbox> </td> </tr> <tr> <td> attach file: </td> <td> <asp:fileupload id="fileupload1" runat="server" /> </td> </tr> <tr> <td valign="top"> body: </td> <td> <asp:textbox id="txtbody" runat="server" textmode="multiline" columns="30" rows="10" ></asp:textbox> </td> </tr> <tr> <td> </td> <td> <asp:button id="btnsubmit" text="send" runat="server" onclick="btnsubmit_click" /> </td> </tr> </table> </div> 

and here code behind:

try {     mailmessage msg = new mailmessage();     // sender e-mail address.     msg.from = new mailaddress(txtusername.text);     // recipient e-mail address.     msg.to.add(txtto.text);     msg.subject = txtsubject.text;     // file upload path     string filename = fileupload1.postedfile.filename;     string mailbody = txtbody.text + "<br/><img src=cid:companylogo>";     linkedresource myimage = new linkedresource(filename);     // create html view     alternateview htmlmail = alternateview.createalternateviewfromstring(mailbody, null, "text/html");     // set contentid property. value of contentid property must same     // src attribute of image tag in email body.      myimage.contentid = "companylogo";     htmlmail.linkedresources.add(myimage);     msg.alternateviews.add(htmlmail);     // remote smtp server ip.     smtpclient smtp = new smtpclient();     smtp.host = "smtp.gmail.com";     smtp.port = 587;     smtp.credentials = new system.net.networkcredential(txtusername.text, txtpwd.text);     smtp.enablessl = true;     smtp.send(msg);     msg = null;     page.registerstartupscript("usermsg", "<script>alert('mail sent thank you...');if(alert){ window.location='sendmail.aspx';}</script>"); } catch (exception ex) {     console.writeline("{0} exception caught.", ex); } 

however line

page.registerstartupscript("usermsg", "<script>alert('mail sent thank you...');if(alert){ window.location='sendmail.aspx';}</script>"); 

gives me error saying:

registerstartupscript(string,string) obsolete.

any idea , how solve it? thank you!

try

using system; using system.net.mail; using system.io;   protected void page_load(object sender, eventargs e)     {      }     protected void btnsubmit_click(object sender, eventargs e)     {         try         {             mailmessage msg = new mailmessage();             // sender e-mail address.             msg.from = new mailaddress(txtusername.text);             // recipient e-mail address.             msg.to.add(txtto.text);             msg.subject = txtsubject.text;             // file upload path             string filename = fileupload1.postedfile.filename;             string mailbody = txtbody.text + "<br/><img          src=cid:companylogo>";             string filename = path.getfilename(filename);             msg.attachments.add(new attachment(fileupload1.postedfile.inputstream, filename));             //linkedresource myimage = new linkedresource(filename);             // create html view             alternateview htmlmail = alternateview.createalternateviewfromstring(mailbody, null, "text/html");             // set contentid property. value of contentid property must same             // src attribute of image tag in email body.              //myimage.contentid = "companylogo";            // htmlmail.linkedresources.add(myimage);             msg.alternateviews.add(htmlmail);             // remote smtp server ip.             smtpclient smtp = new smtpclient();             smtp.host = "smtp.gmail.com";             smtp.port = 587;             smtp.credentials = new system.net.networkcredential(txtusername.text, txtpwd.text);             smtp.enablessl = true;             smtp.send(msg);              msg = null;             //clientscript.registerstartupscript( "<script>alert('mail sent thank you...');if(alert){ window.location='sendmail.aspx';}</script>");             response.write("<script>alert('email sent');</script>");           }         catch (exception ex)         {             response.write("<script>alert('unable send email');</script>");              console.writeline("{0} exception caught.", ex);         }     }