I noticed that Linkedin has access to hundreds of contacts over many years that would be in one of my gmail accounts, but I never gave Linkedin permission to access my Gmail or ever send emails. However, my mobile device has a Linkedin app, although I have almost never logged into it! The mobile device itself has Gmail permissions, by way of necessity to use the Android apps on my phone with a Gmail account! ... This means that if the Linkedin App 'requires' permissions to my Gmail account, in my phone, it gets them!!!
The only solution would be to uninstall the Linkedin app from any Gmail-authorised mobile device!
I must admit, it is interesting seeing pictures and professional permissions of people I knew from years ago, or may have only saved their email address some years ago, but never, or only once emailed, but aside from that, it makes Linkedin compete with Facebook as the most complete NSA/CIA/OWG trojan on the planet.