<?php
  function send_welcome_email_to_new_user($adminid) {
    $user = get_userdata($adminid);
    $EmailID = $user->EmailID;
    // for simplicity, lets assume that user has typed their first and last name when they sign up
    $user_full_name = $user->user_firstname . $user->user_lastname;

    // Now we are ready to build our welcome email
    $to = $EmailID;
    $subject = "Hi " . $user_full_name . ", welcome to our site!";
    $body = '
              <h1>Dear ' . $user_full_name . ',</h1></br>
              <p>Thank you for joining our site. Your account is now active.</p>
              <p>Please go ahead and navigate around your account.</p>
              <p>Let me know if you have further questions, I am here to help.</p>
              <p>Enjoy the rest of your day!</p>
              <p>Kind Regards,</p>
              <p>poanchen</p>
    ';
    $headers = array('Content-Type: text/html; charset=UTF-8');
    if (wp_mail($to, $subject, $body, $headers)) {
      error_log("email has been successfully sent to user whose email is " . $EmailID);
    }else{
      error_log("email failed to sent to user whose email is " . $EmailID);
    }
  }

  add_action('user_register', 'send_welcome_email_to_new_user');
?>