To learn what External sources are, please start with this article. If you wish to add external sources to your marketing campaigns, you'll learn the details here.
Once you have configured external sources, you can proceed to add them to the template from the left side menu in Signature templates.
1) Click on it, you'll have an option to see and add the content from external sources (RSS, Twitter, Eventbrite).
2) Choose how should the formatting of the external source look. It includes a Condition by default.
3) Once you choose an option and click OK, the external source placeholder will be added to your template.
4) What content will later be displayed can be set in the Company profile where you assign the specific external source.
Similar to other placeholders, you can design external sources placeholders to fit your signatures; changing the font to bold or italics, their assigned Style, etc.
Please find a live guide under this link.
If you're not happy with the predefined options, please let us know at email@example.com and we will be happy to come up with a more elaborate result.