No, the system will not send them an email automatically when they are imported. It is up to you to send them an email when you are ready.
If you have not imported subscriptions, then we recommend that you send them the prepared email or create your own email. If you create your own, include the [sign_in_details] tag, which will give them their login details.
If you have imported subscriptions, then we recommend that you send them the subscription renewal email.
