Current Pipechimp version is personal. It means that if you install Pipechimp, only your own contacts are synced between Pipedrive and MailChimp.
You may have multiple users in the same Pipedrive company account. Everyone needs to install Pipechimp to sync their contacts.
Email is a compulsory field in MailChimp so contact persons without a valid email are not copied. If You don’t want all contact persons to be copied you can change Pipedrive ownership to user who don’t have an active Pipechimp account / integration. You can use contact persons data to segment / limit Your MailChimp campaigns.
Pipechimp 2.0 will have company-wide sync which syncs all company contacts from one Pipechimp account: https://www.pipechimp.com/pipechimp/we-are-building-a-new-pipechimp-2-0/