I was researching email deliverability issues the other day… I wanted to confirm my suspicion that Gmail.com, Outlook.com, Yahoo Email, etc were tracking which links I click on from my email. After inspecting the source code I concluded that they are. Google search results returned to helpful links after searching for "are email companies tracking which links I click on in my email?". 

I am assuming that they are tracking which links are clicked on in order to build a database of information to better prevent spam. 
Outlook also claims that they track user response and behavior of email viewers to better prevent spam.
I'm guessing the more an email message is interacted with (  links clicked on, number of times opened, view duration, etc ) the better it looks in the eyes of the spam filter.