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 http://drupalvm.dev:8025/ (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.