Send multiple Emails to selected (checked) ASP.Net GridView rows using C# and VB.Net

Hi ihechi.

Please refer below sample code.

HTML

<img class="img-responsive" style="margin: auto; width: 100%;" src="../images/Header.png" alt="" width="1177" height="168" usemap="#Map" />
<br />
<br />
<div style="margin-left: 300px;">
<asp:Label ID="lblTotal" runat="server" Style="font-size: 14px; font-weight: 600; color: firebrick;" Text="Label"></asp:Label><br />
<br />
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false" AllowPaging="true" PageSize="3"
    OnPageIndexChanging="OnPageIndexChanging">
    <Columns>
        <asp:TemplateField HeaderText="Select All">
            <HeaderTemplate>
                <asp:CheckBox ID="chkAll" runat="server" />
            </HeaderTemplate>
            <ItemTemplate>
                <asp:CheckBox ID="chkSelect" runat="server" />
            </ItemTemplate>
        </asp:TemplateField>
        <asp:BoundField DataField="mailID" HeaderText="Id" ItemStyle-Width="30" />
        <asp:BoundField DataField="FullName" HeaderText="Name" ItemStyle-Width="150" />
        <asp:TemplateField HeaderText="Email">
            <ItemTemplate>
                <asp:HyperLink ID="lnkEmail" runat="server" Text='<%# Eval("Email") %>' NavigateUrl='<%# Eval("Email", "mailto:{0}") %>' />
            </ItemTemplate>
        </asp:TemplateField>
    </Columns>
</asp:GridView>
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script type="text/javascript">
    $("[id*=GridView1] [id*=chkAll]").on("click", function () {
        //Get the reference of Header CheckBox.
        var chkAll = $(this);

        //Loop through all GridView CheckBoxes except Header CheckBox.
        $("[id*=GridView1] [id*=chkSelect]").not("[id*=chkAll]").each(function () {
            $(this)[0].checked = chkAll[0].checked;
        });
    });
</script>
<script type="text/javascript">
    $("[id*=GridView1] [id*=chkSelect]").on("click", function () {
        //Get the reference of Header CheckBox.
        var chkAll = $("[id*=GridView1] [id*=chkAll]");

        //Set Header CheckBox checked to true.
        chkAll[0].checked = true;

        //Loop through all GridView CheckBoxes except Header CheckBox.
        $("[id*=GridView1] [id*=chkSelect]").not("[id*=chkAll]").each(function () {
            if (!$(this).is(":checked")) {
                chkAll[0].checked = false;
                return;
            }
        });
    });
</script>
<br />
<asp:Button Text="Send Email Reminder" runat="server" OnClick="SendReminderEmail" /><br />
<%--  <asp:Panel ID="pnlThankYouMessage" runat="server" Visible="False">
Email successfully sent
</asp:Panel>--%>
</div>

Namespace

C#

using System.Collections;
using System.Data;
using System.Threading.Tasks;
using System.Net.Mail;

VB.Net

Imports System.Collections
Imports System.Data
Imports System.Threading.Tasks
Imports System.Net.Mail

Code

C#

protected void Page_Load(object sender, EventArgs e)
{
    ArrayList checkboxArray;
    if (ViewState["CheckBoxArray"] == null)
    {
        checkboxArray = new ArrayList();
    }
    else
    {
        checkboxArray = (ArrayList)ViewState["CheckBoxArray"];
    }

    if (this.IsPostBack)
    {
        int checkBoxIndex;
        bool checkAllWasChecked = false;
        CheckBox chkAll = (CheckBox)GridView1.HeaderRow.Cells[0].FindControl("chkAll");
        string checkAllIndex = "chkAll-" + GridView1.PageIndex;
        if (chkAll.Checked)
        {
            if (checkboxArray.IndexOf(checkAllIndex) == -1)
            {
                checkboxArray.Add(checkAllIndex);
            }
        }
        else
        {
            if (checkboxArray.IndexOf(checkAllIndex) != -1)
            {
                checkboxArray.Remove(checkAllIndex);
                checkAllWasChecked = true;
            }
        }
        for (int i = 0; i < GridView1.Rows.Count; i++)
        {
            if (GridView1.Rows[i].RowType == DataControlRowType.DataRow)
            {
                CheckBox chk = (CheckBox)GridView1.Rows[i].Cells[0].FindControl("chkSelect");
                checkBoxIndex = GridView1.PageSize * GridView1.PageIndex + (i + 1);
                if (chk.Checked)
                {
                    if (checkboxArray.IndexOf(checkBoxIndex) == -1 && !checkAllWasChecked)
                    {
                        checkboxArray.Add(checkBoxIndex);
                    }
                }
                else
                {
                    if (checkboxArray.IndexOf(checkBoxIndex) != -1 || checkAllWasChecked)
                    {
                        checkboxArray.Remove(checkBoxIndex);
                    }
                }
            }
        }
    }
    ViewState["CheckBoxArray"] = checkboxArray;
    GridView1.DataSource = LoadData();
    GridView1.DataBind();
    lblTotal.Text = GridView1.Rows.Count.ToString() + " members have yet to complete the form";
}

protected void OnPageIndexChanging(object sender, GridViewPageEventArgs e)
{
    GridView1.PageIndex = e.NewPageIndex;
    GridView1.DataBind();
    if (ViewState["CheckBoxArray"] != null)
    {
        ArrayList CheckBoxArray = (ArrayList)ViewState["CheckBoxArray"];
        string checkAllIndex = "chkAll-" + GridView1.PageIndex;

        if (CheckBoxArray.IndexOf(checkAllIndex) != -1)
        {
            CheckBox chkAll = (CheckBox)GridView1.HeaderRow.Cells[0].FindControl("chkAll");
            chkAll.Checked = true;
        }
        for (int i = 0; i < GridView1.Rows.Count; i++)
        {
            if (GridView1.Rows[i].RowType == DataControlRowType.DataRow)
            {
                if (CheckBoxArray.IndexOf(checkAllIndex) != -1)
                {
                    CheckBox chk = (CheckBox)GridView1.Rows[i].Cells[0].FindControl("chkSelect");
                    chk.Checked = true;
                }
                else
                {
                    int CheckBoxIndex = GridView1.PageSize * (GridView1.PageIndex) + (i + 1);
                    if (CheckBoxArray.IndexOf(CheckBoxIndex) != -1)
                    {
                        CheckBox chk = (CheckBox)GridView1.Rows[i].Cells[0].FindControl("chkSelect");
                        chk.Checked = true;
                    }
                }
            }
        }
    }
}

protected DataTable LoadData()
{
    DataTable dt = new DataTable();
    dt.Columns.AddRange(new DataColumn[3] {
        new DataColumn("mailID", typeof(int)),
        new DataColumn("FullName", typeof(string)),
        new DataColumn("Email", typeof(string))
    });
    dt.Rows.Add("1001", "Nick Fury", "shield@gmail.com");
    dt.Rows.Add("1002", "Robert DownleyJr", "ironman@gmail.com");
    dt.Rows.Add("1003", "Andrew Garfield", "spidey@gmail.com");
    dt.Rows.Add("1004", "Chris Evan", "captain@gmail.com");
    dt.Rows.Add("1005", "Bruce Banner", "hulk@gmail.com");
    dt.Rows.Add("1006", "Chris Hemsworth", "thor@gmail.com");
    return dt;
}

protected void SendReminderEmail(object sender, EventArgs e)
{
    // Create a temporary DataTable
    DataTable dtCustomers = new DataTable();
    dtCustomers.Columns.AddRange(new DataColumn[2] {
        new DataColumn("fullName", typeof(string)),
        new DataColumn("email", typeof(string))
    });

    GridView1.AllowPaging = false;
    GridView1.DataBind();
    // 'Copy the Checked Rows to DataTable
    ArrayList checkboxArray = (ArrayList)ViewState["CheckBoxArray"];
    int index = 1;
    foreach (GridViewRow row in GridView1.Rows)
    {
        if (checkboxArray.Contains(index))
        {
            dtCustomers.Rows.Add(row.Cells[2].Text, (row.FindControl("lnkEmail") as HyperLink).Text);
        }
        index++;
    }
    GridView1.AllowPaging = true;
    GridView1.DataBind();

    string subject = "Completion Reminder";
    string body = "Hello {0},<br /><br />Please remember to complete the form before deadline.<br /><br />Thanks.";

    // Using Parallel Multi-Threading send multiple bulk email.
    Parallel.ForEach(dtCustomers.AsEnumerable(), row =>
    {
        SendEmail(row["email"].ToString(), subject, string.Format(body, row["fullName"]));
    });
}

private bool SendEmail(string recipient, string subject, string body)
{
    MailMessage mm = new MailMessage();
    mm.To.Add(recipient);
    MailAddress EmailSender = new MailAddress("myemail@domain.com");
    mm.From = EmailSender;
    mm.Subject = subject;
    mm.Body = body;
    mm.IsBodyHtml = true;
    SmtpClient smtp = new SmtpClient();
    // Configure an SmtpClient to send the mail.
    SmtpClient client = new SmtpClient("smtp.hostname.com");
    client.EnableSsl = false;
    client.Send(mm);
    return true;
}

VB.Net

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
    Dim checkboxArray As ArrayList

    If ViewState("CheckBoxArray") Is Nothing Then
        checkboxArray = New ArrayList()
    Else
        checkboxArray = CType(ViewState("CheckBoxArray"), ArrayList)
    End If

    If Me.IsPostBack Then
        Dim checkBoxIndex As Integer
        Dim checkAllWasChecked As Boolean = False
        Dim chkAll As CheckBox = CType(GridView1.HeaderRow.Cells(0).FindControl("chkAll"), CheckBox)
        Dim checkAllIndex As String = "chkAll-" & GridView1.PageIndex

        If chkAll.Checked Then
            If checkboxArray.IndexOf(checkAllIndex) = -1 Then
                checkboxArray.Add(checkAllIndex)
            End If
        Else

            If checkboxArray.IndexOf(checkAllIndex) <> -1 Then
                checkboxArray.Remove(checkAllIndex)
                checkAllWasChecked = True
            End If
        End If

        For i As Integer = 0 To GridView1.Rows.Count - 1
            If GridView1.Rows(i).RowType = DataControlRowType.DataRow Then
                Dim chk As CheckBox = CType(GridView1.Rows(i).Cells(0).FindControl("chkSelect"), CheckBox)
                checkBoxIndex = GridView1.PageSize * GridView1.PageIndex + (i + 1)
                If chk.Checked Then
                    If checkboxArray.IndexOf(checkBoxIndex) = -1 AndAlso Not checkAllWasChecked Then
                        checkboxArray.Add(checkBoxIndex)
                    End If
                Else

                    If checkboxArray.IndexOf(checkBoxIndex) <> -1 OrElse checkAllWasChecked Then
                        checkboxArray.Remove(checkBoxIndex)
                    End If
                End If
            End If
        Next
    End If

    ViewState("CheckBoxArray") = checkboxArray
    GridView1.DataSource = LoadData()
    GridView1.DataBind()
    lblTotal.Text = GridView1.Rows.Count.ToString() & " members have yet to complete the form"
End Sub

Protected Sub OnPageIndexChanging(ByVal sender As Object, ByVal e As GridViewPageEventArgs)
    GridView1.PageIndex = e.NewPageIndex
    GridView1.DataBind()

    If ViewState("CheckBoxArray") IsNot Nothing Then
        Dim CheckBoxArray As ArrayList = CType(ViewState("CheckBoxArray"), ArrayList)
        Dim checkAllIndex As String = "chkAll-" & GridView1.PageIndex
        If CheckBoxArray.IndexOf(checkAllIndex) <> -1 Then
            Dim chkAll As CheckBox = CType(GridView1.HeaderRow.Cells(0).FindControl("chkAll"), CheckBox)
            chkAll.Checked = True
        End If

        For i As Integer = 0 To GridView1.Rows.Count - 1
            If GridView1.Rows(i).RowType = DataControlRowType.DataRow Then
                If CheckBoxArray.IndexOf(checkAllIndex) <> -1 Then
                    Dim chk As CheckBox = CType(GridView1.Rows(i).Cells(0).FindControl("chkSelect"), CheckBox)
                    chk.Checked = True
                Else
                    Dim CheckBoxIndex As Integer = GridView1.PageSize * (GridView1.PageIndex) + (i + 1)

                    If CheckBoxArray.IndexOf(CheckBoxIndex) <> -1 Then
                        Dim chk As CheckBox = CType(GridView1.Rows(i).Cells(0).FindControl("chkSelect"), CheckBox)
                        chk.Checked = True
                    End If
                End If
            End If
        Next
    End If
End Sub

Protected Function LoadData() As DataTable
    Dim dt As DataTable = New DataTable()
    dt.Columns.AddRange(New DataColumn(2) {New DataColumn("mailID", GetType(Integer)), New DataColumn("FullName", GetType(String)), New DataColumn("Email", GetType(String))})
    dt.Rows.Add("1001", "Nick Fury", "shield@gmail.com")
    dt.Rows.Add("1002", "Robert DownleyJr", "ironman@gmail.com")
    dt.Rows.Add("1003", "Andrew Garfield", "spidey@gmail.com")
    dt.Rows.Add("1004", "Chris Evan", "captain@gmail.com")
    dt.Rows.Add("1005", "Bruce Banner", "hulk@gmail.com")
    dt.Rows.Add("1006", "Chris Hemsworth", "thor@gmail.com")
    Return dt
End Function

Protected Sub SendReminderEmail(ByVal sender As Object, ByVal e As EventArgs)
    Dim dtCustomers As DataTable = New DataTable()
    dtCustomers.Columns.AddRange(New DataColumn(1) {New DataColumn("fullName", GetType(String)), New DataColumn("email", GetType(String))})
    GridView1.AllowPaging = False
    GridView1.DataBind()
    Dim checkboxArray As ArrayList = CType(ViewState("CheckBoxArray"), ArrayList)
    Dim index As Integer = 1

    For Each row As GridViewRow In GridView1.Rows
        If checkboxArray.Contains(index) Then
            dtCustomers.Rows.Add(row.Cells(2).Text, (TryCast(row.FindControl("lnkEmail"), HyperLink)).Text)
        End If
        index += 1
    Next
    GridView1.AllowPaging = True
    GridView1.DataBind()
    Dim subject As String = "Completion Reminder"
    Dim body As String = "Hello {0},<br /><br />Please remember to complete the form before deadline.<br /><br />Thanks."
    Parallel.ForEach(dtCustomers.AsEnumerable(),
                        Function(row)
                            Return SendEmail(row("email").ToString(), subject, String.Format(body, row("FullName")))
                        End Function)
End Sub

Private Function SendEmail(ByVal recipient As String, ByVal subject As String, ByVal body As String) As Boolean
    Dim mm As MailMessage = New MailMessage()
    mm.[To].Add(recipient)
    Dim EmailSender As MailAddress = New MailAddress("myemail@domain.com")
    mm.From = EmailSender
    mm.Subject = subject
    mm.Body = body
    mm.IsBodyHtml = True
    Dim smtp As SmtpClient = New SmtpClient()
    Dim client As SmtpClient = New SmtpClient("smtp.hostname.com")
    client.EnableSsl = False
    client.Send(mm)
    Return True
End Function

Screenshot