What is an inactive contact?
Inactive contacts are the contacts that have an invalid email address or are marked as inactive by users. When a contact is inactive, you can see the inactive status in the individual page or in the contact list.
Why does inactive contact matter?
Unlike archived contacts, inactive contacts are still in your Contacts tab, but you cannot send smart mails to them. Even if you try to add them to a smart mail, you will get the Cannot send email to an inactive contact error message.
How to make a contact inactive / active?
There are two situations where a contact becomes invalid:
1) When the contacts are bounced back from a smart mail, the system automatically makes them inactive as their email addresses are no longer valid.
2) You can make contacts inactive manually by clicking on the three dot icon under the contact profile picture > Make Contact Inactive.
Whether the contact is made inactive automatically or manually, you can always make it active again by going to the individual page and clicking on Make Contact Active.