Context: You are installing a Tiki in a secure environment and by default, Tiki can't connect to the web. Below is a list of URLs to white-list and why.
php temp/composer.phar diagnose
By default, Tiki will use the server's sendmail (via PHP). If this is not configured, please see: SMTP
There is a call to Google Chart API to make a pie chart in the performance admin panel (the byte code cache tab of the tiki-admin.php?page=performance). Ex.: https://chart.googleapis.com/chart?cht=p3&chs=250x100&chd=t%3A0.76%2C0.24&chl=Used%7CAvailable&chtt=Memory todo: replace this by a Tiki generated pie chart fixed in 18.4 and 19.2
Tiki policy with respect to external links