LinkedIn makes it really easy to import contacts from your mail system, and does not send annoying automatic emails to your contacts. Instead, LinkedIn will display your list of your contacts, including details about who is already using LinkedIn and how many contacts they have, and then you can manually click the boxes for the boxes for the people you want to send connection invitations to.

To import contacts, visit your LinkedIn profile and click on “add connections” in the upper right corner. Follow the steps to import contacts from whatever email system you use.