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).

Disable MailHog

If you don't want to use MailHog, you can set the following override (back to PHP's default, as defined in the geerlingguy.php role) in your config.yml file:

php_sendmail_path: "/usr/sbin/sendmail -t -i"

After doing this, you can also prevent MailHog's installation by removing mailhog from the installed_extras list.

For a list of available role variables, see the geerlingguy.mailhog Ansible role's README.