Contact summary email link open mailto: instead?
For many people, this new behavior is an improvement, but there are definitely others who preferred the old approach.

The operative line in the template is here, and the only way you don't see that is if outbound mail is turned off on the site.  (In a perfect world, there would be a site-wide setting for this.)

If you want a customization to handle this, the easiest might be to add a bit of jQuery via a .extra.tpl, extension, or theme:

CRM.$(function($) {
  $('.crm-contact_email a.crm-popup').each(function() {
    var email = $.trim($(this).html());
    var emailLink = $('&lt;a/&gt;', {
      class: 'mailto-link',
      href: 'mailto:' + email,
      title: ts('Send an email outside of CiviCRM'),
      html: '&lt;i class="crm-i fa-envelope"&gt;&lt;/i&gt;'
    });
    $(this).after(emailLink);
  });
});