Email Security Exception in ASP.NET - asp.net

Question

Security ExceptionDescription: The application attempted to perforanoperation not allowed by`the security policy. To grant this application the required permission please contact your system administrator or change the application's trust level in the configuration file.
Exception Details: System.Security.SecurityException: Request for the permission of type 'System.Net.Mail.SmtpPermission, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.
Source Error:
Line 45: {
Line 46: smtp.Host = "smtp.gmail.com";
Line 47: smtp.Port = 587;
Line 48: smtp.EnableSsl = true;
Line 49: smtp.DeliveryMethod = System.Net.Mail.SmtpDeliveryMethod.Network;
Source File: d:\inetpub\vhosts\softsoftware.in\designscentre\asktheexpert.aspx.cs Line: 47
Stack Trace:
[SecurityException: Request for the permission of type 'System.Net.Mail.SmtpPermission, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089' failed.]
System.Security.CodeAccessSecurityEngine.Check(Object demand, StackCrawlMark& stackMark, Boolean isPermSet) +0
System.Security.CodeAccessPermission.Demand() +61
System.Net.Mail.SmtpClient.set_Port(Int32 value) +106
asktheexpert.sendbtn_Click(Object sender, EventArgs e) in d:\inetpub\vhosts\softsoftware.in\designscentre\asktheexpert.aspx.cs:47
System.Web.UI.WebControls.Button.OnClick(EventArgs e) +111
System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +110
System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +6785
System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +242
System.Web.UI.Page.ProcessRequest() +80
System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +21
System.Web.UI.Page.ProcessRequest(HttpContext context) +49
ASP.asktheexpert_aspx.ProcessRequest(HttpContext context) in App_Web_vkk6wpqv.2.cs:0
System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +181
System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75
Version Information: Microsoft .NET Framework Version:2.0.50727.5485; ASP.NET Version:2.0.50727.5483
Security ExceptionDescription: The application attempted to perforanoperation not allowed by`the security policy. To grant this application the required permission please contact your system administrator or change the application's trust level in the configuration file.
website work in Localhost correctly.
but Error on server .
Please Help me how to solve this error.