VERIFIED SOLUTION i

Learn to use conditional logic for a template containing one or more documents to use as an e-mail body or attachment in EngageOne Digital Delivery

This can be achieved using 'Document Selector'. To use Document Selector, it needs to be specified it at EngageOne Designer and at EngageOne Server Level.
For Example, if one Document need to send as email and another document need to send as email attachment.

Condition in EngageOne Designer for email body:
User-added image

Condition in EngageOne Designer for email attachment:
User-added image

Condition in EngageOne Server for email body:
User-added image

Condition in EngageOne Server for email attachment:
User-added image

For more information on Document Selector, refer section 'Delivery management' in 'EngageOne Administrative Guide' shipped with the installer.
UPDATED:  July 20, 2017