How to Reuse the Method or Function in Different Pages for Sending Emails ASP.Net

You can create a class. In that class you can have a method called SendEmail with some parameter like

public class Email
{
    public Email()
    {
        //
        // TODO: Add constructor logic here
        //
    }

    public void SendEmail(string receiverEmail, string subject, string body)
    {
        //Write some code
    }
}

After that create an object of that class and call that method in Button Onclick Event

HTML

<asp:Button Text="Send Email" OnClick="SendEmail" runat="server" />

Button Event

protected void SendEmail(object sender, EventArgs e)
{
    Email email = new Email();
    email.SendEmail("test@test.com", "subject", "body");
}