it is an email marketing site such as mail chimp
Klaviyo is a tool that makes personalized marketing a breeze through data-driven decision making. In the past, only massive companies had the resources to create highly personalized messaging. Klaviyo brings those capabilities with an intuitive interface that a one-person startup can easily manage, to more detailed customization a large or enterprise company can develop with their marketing team.
They do have an unofficial integration with us at this time through Zapier https://zapier.com/apps/klaviyo/integrations/shipstation