Disable validation on Button Click in ASP.Net

I am trying to check emaail by verification code send to email id od user while registration but when I enter email and click on send code button then validation occur...

I cant remove validation but I want that validation Validate after verifying the email process.

I tried to set cause validation false initially and from code behind I set it True but it is still not working.

Please help Me.

Thanks

<h1>
    Registration Here</h1>
<p>
    Name</p>
<asp:TextBox class="form-control" ID="name" placeholder="Enter Name" runat="server"
    Style="font-size: x-large" CausesValidation="false"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator5" runat="server" ErrorMessage="Required"
    ForeColor="Red" ControlToValidate="name"></asp:RequiredFieldValidator>
<p>
    Email</p>
<asp:TextBox class="form-control" ID="mail" placeholder="Enter Email" runat="server"
    Style="font-size: x-large" CausesValidation="false"></asp:TextBox>
<asp:Panel runat="server" ID="pnlbtn">
    <asp:Button CssClass="btn btn-success" ID="btnsend" Style="font-size: x-large" runat="server"
        Text="Send Activation code." OnClick="btnsend_Click"></asp:Button>
</asp:Panel>
<asp:RequiredFieldValidator ID="RequiredFieldValidator1" runat="server" ErrorMessage="Required"
    ForeColor="Red" ControlToValidate="mail"></asp:RequiredFieldValidator>
<asp:Panel runat="server" ID="pnlacti" Visible="false">
    <asp:TextBox class="form-control" ID="txtacti" placeholder="Enter Activation code."
        runat="server" Style="font-size: x-large"></asp:TextBox>
    <asp:Button CssClass="btn btn-success" ID="txtverify" Style="font-size: x-large"
        runat="server" Text="Verify Email" OnClick="txtverify_Click"></asp:Button>
</asp:Panel>
<asp:Panel runat="server" ID="pnll" Visible="false">
    <asp:Label CssClass="label label-info" ID="Label1" runat="server" Font-Size="Large"
        ForeColor="#00cc00" BackColor="White"></asp:Label><br />
    <br />
</asp:Panel>
<p>
    Password</p>
<asp:TextBox class="form-control" ID="pass" placeholder="Enter Password" CausesValidation="false"
    runat="server" TextMode="Password" Style="font-size: x-large"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator4" runat="server" ErrorMessage="Required"
    ForeColor="Red" ControlToValidate="pass"></asp:RequiredFieldValidator>
<p>
    Confirm Password</p>
<asp:TextBox class="form-control" ID="cpass" placeholder="Re-Type Password" CausesValidation="false"
    runat="server" TextMode="Password" Style="font-size: x-large"></asp:TextBox>
<asp:RequiredFieldValidator ID="RequiredFieldValidator7" runat="server" ControlToValidate="cpass"
    ErrorMessage="Password confirmation is required!" SetFocusOnError="True" Display="Dynamic"
    ForeColor="Red" />
<asp:CompareValidator ID="comparePasswords" runat="server" ControlToCompare="pass"
    ControlToValidate="cpass" ErrorMessage="Your passwords do not match up!" Display="Dynamic"
    ForeColor="Red" />
<p>
    Role:</p>
<asp:RadioButtonList ID="rbtRole" runat="server" CausesValidation="false" RepeatDirection="Vertical"
    CssClass="radio btn-group-justified" Font-Bold="true" Font-Size="Large">
    <asp:ListItem>Service Seeker</asp:ListItem>
    <asp:ListItem>Service Provider</asp:ListItem>
    <asp:ListItem>Company</asp:ListItem>
    <asp:ListItem>Job Seeker</asp:ListItem>
</asp:RadioButtonList>
<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ErrorMessage="Select role"
    ForeColor="Red" ControlToValidate="rbtRole"></asp:RequiredFieldValidator>
<asp:Button CssClass="btn btn-success" ID="btnLogin" Style="font-size: x-large" runat="server"
    Text="Submit" OnClick="btnLogin_Click"></asp:Button>
</br> </br> </div>