Alow SSL conections to sites with self-signed or problematic certificates

wp_mail_smtp_custom_options.php

<?php

add_filter('wp_mail_smtp_custom_options', function( $phpmailer ) {
  $phpmailer->SMTPOptions = array(
    'ssl' => array(
      'verify_peer' => false,
      'verify_peer_name' => false,
      'allow_self_signed' => true
    )
  );
} );