If you're not exactly sure what are "external sources", where and how to configure them, please follow to this article. If you wish to add external sources to your signature template, you'll learn the details here.
Once you've prepared your marketing Set and Campaigns, you can start populating them. The external sources are an easy way to manage the content of your campaigns, especially when combined with rotating campaigns.
You can start adding content from external sources by clicking on the button Ext. sources in the Campaign view.
If you click on it, you'll have an option to see and add the content from external sources (RSS, Twitter, Eventbrite).
As you can see for yourself, we offer you several options how to present this content - as a bare link, headline or HTML fragment. Once you choose an option and click OK, the external source placeholder will be added to your template.
Similar to other placeholders, you can design external sources placeholders to fit your signatures; changing the font to bold or italics, adding colors or other changes will be reflected in the final signature as well.