Salesforce tracked merges are logged back into salesforce as well as EmailCaddie website. EmailCaddie
records sent , open and click events on an email into Salesforce.
EmailCaddie automatically logs the merge’s sent under the contact’s activity history and also account activity history (if contact is linked to an account).
EmailCaddie provides instant desktop notification
Likewise it provides information on the Timeline. Click on the salesforce icon to view the email open information in Salesforce.
Email Open event is logged into the contact's activity history in Salesforce.
Articles that will be of your interest:
Getting started with Salesforce
Quick access to EmailCaddie website
How to merge with Salesforce
How to Re Merge using EmailCaddie How to view EmailMerge tracking information