Why selected row is not deleting

protected void Button1_Click(object sender, EventArgs e)
    {
        //Loop through all the rows in gridview
        foreach (GridViewRow gvrow in gv1.Rows)
        {
            //Finiding checkbox control in gridview for particular row
            CheckBox chkdelete = (CheckBox)gvrow.FindControl("chkdelete");
            //Condition to check checkbox selected or not
            if (chkdelete.Checked)
            {
                //Getting email of particular row using datakey value
                //int mail = Convert.ToInt32(gv1.DataKeys[gvrow.RowIndex].Value);
                string email = gv1.DataKeys[gvrow.RowIndex]["mail"].ToString();
                AccessDataSource1.DeleteParameters["mail"].DefaultValue = email;
                AccessDataSource1.Delete();
            }
        }

    }

<asp:GridView ID="gv1" runat="server" DataSourceID="AccessDataSource1"
DataKeyNames="mail" CssClass="Gridview" AutoGenerateColumns="False"
HeaderStyle-BackColor="#61A6F8" HeaderStyle-Font-Bold="true"
HeaderStyle-ForeColor="White" AllowPaging="True">
<Columns>
<asp:TemplateField>
<ItemTemplate>
<asp:CheckBox ID="chkdelete" runat="server"/>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="cname" HeaderText="NAME" />
<asp:BoundField DataField="dob" HeaderText="DOB" />
<asp:BoundField DataField="city" HeaderText="CITY" />
<asp:BoundField DataField="mail" HeaderText="EMAIL" />
<asp:BoundField DataField="occu" HeaderText="OCCUPATION" />
</Columns>
</asp:GridView>
                        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Delete" />
                        <br />
                        <asp:AccessDataSource ID="AccessDataSource1" runat="server"
                            DataFile="~/Rabiya.mdb"
                            SelectCommand="SELECT [cname], [dob], [city], [mail], [occu] FROM [joining]" DeleteCommand="Delete from joining where mail=@mail">
            <DeleteParameters>
            <asp:Parameter Name="mail" Type="Int32" />
            </DeleteParameters>
                        </asp:AccessDataSource>

<script type="text/javascript">
    function Confirmationbox() {
        var result = confirm('Are you sure you want to delete selected User(s)?');
        if (result) {
            return true;
        }
        else {
            return false;
        }
    }
</script>