Sitebulb has a range of 'global settings' which act as the default settings for every new audit you start. From the Dashboard, choose the 'Settings' option from the left-hand menu.
From here, the 'Excluded External URLs' tab allows you to exclude Sitebulb from scheduling and crawling specific external URLs, by defining domains, paths and patterns.
You will find a number of values pre-set, which are mostly used to stop Sitebulb crawling thousands of irrelevant URLs (e.g. social share linking URLs). If you want to stop Sitebulb from crawling external URLs or domains, add them to these lists.