HI @pant.amit, welcome to the community!

As far as I know, there isn’t a way to Trigger a Flow from a Campaign based on Campaign performance metrics and events (Delivered, Opened, Clicked, etc), Klaviyo mentions in the docs that this isn’t yet possible.  

However, you might be able to do parts of this with the Klaviyo API with the “Events API” and filter it to “Received Email” events.  Then for each person that received, you can look up the related message for some of the message data details.  However, from what I remember, it doesn’t appear it includes the actual email body (HTML or Plain Text).  That might be very low level data that isn’t exposed by the API yet - though you can also look at the “Campaign API” to see what data you can retrieve.

With the information in the Campaign API, you also can get the Template ID and you might be able to rebuild each email for each recipient and send it to your third party endpoint, but that’s quite a big lift. 

Perhaps others might have other suggestions on how to do this, also try cross-posting this into our Developer Group here: https://community.klaviyo.com/groups/developer-group-64

Thanks