System.Net.Mail.SmtpFailedRecipientException: Mailbox unavailable. The server response was: 5.7.1 Unable to relay

I have got this issue many times, when I try to send email using smtp. There can be several causes for this. You have to allow relay for mail to be sent to outside servers like gmail.com. For sending mail within your server you don't have to do this. You can find some helps from the following links:
Help1
Help2
Help3

The code I have used is given below:

using System.Net.Mail;


SmtpClient smtpClient = new SmtpClient();
MailMessage message = new MailMessage();
smtpClient.Port = 25;
smtpClient.Host = "smtp.domain.com";
smtpClient.UseDefaultCredentials = false;
smtpClient.Credentials = new System.Net.NetworkCredential("webmail username", "webmail password");
message.From = new MailAddress("webmail username");
message.To.Add("test@gmail.com");
string emailBody = "Hi,

Welcome

";
message.Body = emailBody;
message.Subject = "testing";
message.IsBodyHtml = true;
smtpClient.Send(message);

But, after making the changes on the server, as specified on the above links, I was still getting the same error. Then I added the following line in between the above code.
smtpClient.DeliveryMethod = SmtpDeliveryMethod.PickupDirectoryFromIis;

Then the error was gone.

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I got this issue in my system using Windows 7 Ultimate when trying to run a site which is configured to run in IIS. You can get the solution for this from the following link

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Some times we want to group gridview. ZNet is a good control for this use.
ZNet
We can use this for grouping and also for the comparison.

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specifying ValidationGroup in Page_ClientValidate function

Hi,

We know that, Page_ClientValidate function tests if all controls meet asp.net validation criteria. This function is provided by asp.net. But, if we use more than, one validation group in the page, we may have to specify the validation group, we want to validate. For that, give like given below:
Page_ClientValidate('ValGroupName')

Then, it will validate only for that validation group

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The Controls collection cannot be modified because the control contains code blocks

This is a common error. It occurs when we use <%= %> tag inside the head tag with runat="server" given. You can get rid of the error by removing the runat="server" from the head tag. But, sometimes, we want to keep that. We can use <%# %> instead of <%= %>. But, then, the value may not get bound and we may not get the value of the expression. So, when we use <%# %>, we have to add Page.Header.DataBind(); in the Page Load event.
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To access control of a User Control from an aspx page

Whenever you want to access the controls of an usercontrol, create public properties for those controls in your usercontrols and you could easily access them in your .aspx page.

Here it goes how...
UserControl.

1 public partial class WebUserControl : System.Web.UI.UserControl
2 {
3 public string TextBoxValue {
4 get { return TextBox1.Text; }
5 set { TextBox1.Text = value; }
6 }
7 protected void Page_Load(object sender, EventArgs e) {
8
9 }
10 }

In your .aspx page you can access it either html or code
<%@ Register TagPrefix="DS" TagName="TB" Src="~/WebUserControl.ascx" %>




or

public partial class _Default : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
myTB1.TextBoxValue = "Sample Text";
}
}

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From the following link, you can see all types of formats we can get using DateTime.ToString() method.
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