The Simplenews Mailjet Subscriptions module allows for a simple subscription integration between Simplenews module and Mailjet.

You can subscribe users to your Mailjet list and associate them with a respective property

Configuration:
1 - Add some Simplenews Newsletter first
2 - Go to /admin/config/services/simplenews/mailjet-subscriptions
3 - Add a new Simplenews Maijet Subscription configuration.
4 - Map the property of the Mailjet list (e.g. Category) with the value associated with your Newsletter.