Using the New User Approve Plugin + MemberPress to allow filtered domains through

mepr-nua-approve-by-email-domain.php

<?php
/*
Plugin Name: MemberPress + New User Approve
Version: 1.0.0
Author: Caseproof, LLC
Author URI: http://caseproof.com
Description: Helps the flow of signups from approved/unapproved domains between the MemberPress and New User Approve plugins
*/

function mepr_get_approved_domains() {
  //EDIT this array to match currently allowed domains
  return array( 'aarp.com',
                'abbvie.com',
                'adp.com',
                'amazon.com',
                'astrazeneca.com',
                'averydennison.com'
  );
}

function mepr_ends_with($haystack, $needle) {
  return (($temp = strlen($haystack) - strlen($needle)) >= 0 && strpos($haystack, $needle, $temp) !== false);
}

//Where the bulk of this addon happens
function mepr_check_email_domain($errors) {
  $email = stripslashes($_POST['user_email']);
  $approved_domains = mepr_get_approved_domains();
  $was_approved = false

  foreach($approved_domains as $ad) {
    if(mepr_ends_with($email, $ad)) {
      $was_approved = true;
      $_REQUEST['action'] = 'createuser'; //Set this so "New User Approve" plugin will not limit the subscriber
      break;
    }
  }

  if(!$was_approved) {
    mepr_send_awaiting_approval_email($email);
  }

  return $errors;
}
add_filter('mepr-validate-signup', 'mepr_check_email_domain');

function mepr_send_awaiting_approval_email($email) {
  //EDIT $message if you wish
  $message = "<h4>Thank you for registering for xxxxx!</h4> <p>Your account is pending while we review it. We will send you another email within 48 hours if your account is approved.</p><p>Sincerely,<br/>the AWESOME SITE team</p>";
  
  @wp_mail($email, 'Your account is pending', $message, array("Content-Type: text/html"));
}

//USER APPROVED EMAIL TO USER
function mepr_override_nua_approved_email_message($message, $user) {
  //EDIT $message if you wish
  $message = "<h4>Congratulations, your account has been approved!</h4> <p>Your account at THE AWEOMSE SITE has been approved. <a href=\"http://somesite.com/login/\">Click here to login</a>.</p><p>Sincerely,<br/>the AWESOME SITE team</p>";

  return $message;
}
add_filter('new_user_approve_approve_user_message', 'mepr_override_nua_approved_email_message', 11, 2);

function mepr_override_nua_approved_email_subject($subject) {
  //EDIT $subject if you wish
  $subject = "Your account has been approved";

  return $subject;
}
add_filter('new_user_approve_approve_user_subject', 'mepr_override_nua_approved_email_subject', 11);

//USER DENIED EMAIL TO USER
function mepr_override_nua_denied_email_message($message, $user) {
  //EDIT $message if you wish
  $message = "<h4>Sorry, your account has been denied</h4> <p>Your account has been denied becuase of xyz. If you feel this was in error <a href=\"http://somesite.com/contact/\">please contact us for further assistance</a>.</p><p>Sincerely,<br/>the AWESOME SITE team</p>";

  return $message;
}
add_filter('new_user_approve_deny_user_message', 'mepr_override_nua_denied_email_message', 11, 2);

function mepr_override_nua_denied_email($subject) {
  //EDIT $subject if you wish
  $subject = "Your account has been denied";

  return $subject;
}
add_filter('new_user_approve_deny_user_subject', 'mepr_override_nua_denied_email', 11);

//EMAIL HEADERS OVERRIDE
function mepr_nua_email_headers_override($headers) {
  unset($headers[1]);
  $headers[] = "Content-Type: text/html";
  
  return $headers;
}
add_filter('new_user_approve_email_header', 'mepr_nua_email_headers_override', 3);

//WE DON'T WANT TO OVERRIDE THE PW THE USER SET WHEN SIGNING UP VIA MEMBERPRESS
function mepr_ignore_new_user_autopass() {
  return true;
}
add_filter('new_user_approve_bypass_password_reset', 'mepr_ignore_new_user_autopass');

If you're just looking to modify the emails that are sent out. You can copy these lines into a plugin like My Custom Functions: https://gist.github.com/cartpauj/4141563c14b6ff4fa1a6#file-mepr-nua-approve-by-email-domain-php-L54-L95 and make edits there.