I confirm Linkedin is a vector for spam, the way they handle and publish your email address: I use a dedicated, unique email address for my account, and systematically start receiving unsollicited emails and spam a few days after.

I now have the habit to register a new email address every few months on Linkedin, to track the issue. It's clear and easy to prove that the new email address is used by spammers after a short time. One of the main reasons is probably because once you are connected to someone, he/she can access your profile contact details including email and phone number. My guess is there are bots scraping the contacts to populate their spam databases.

I'm sure most, if not all users of Linkedin don't realize this issue, as they generally register using a non-dedicated email address, preventing them to check the origin of the spam leak.