By default, Drupal VM redirects all PHP emails to MailHog (instead of sending them to the outside world). You can access the MailHog UI at (or whatever domain you have configured in config.yml).

You can override the default behavior of redirecting email to MailHog by editing or removing the php_sendmail_path inside config.yml, and you can choose to not install MailHog at all by removing it from installed_extras in config.yml.