Hi @Shruti1
This addresses the architecture principles for Adobe Campaign and it can be a lengthy topic to discuss,
IN a nutshell:
Marketing: this is the core instance where marketers define and execute their campaigns
Mid-Sourcing: for very large customers and for hybrid hosting model, instance that sends the delivery physically , this instance is also where you would create your transactional message templates and your offers
RT: stands for Real-time aka transactional messages such as forgot password, confirmation messages, etc... instance that send messages in real-time from an event occuring on the 3rd party application
Execution Server: other name for the RT instance. In the context of inbound offer management this is the instance that will actually process the offer request
I invite you to review the online documentation where these are explained
Architecture Principles: https://experienceleague.adobe.com/docs/campaign-classic/using/installing-campaign-classic/architect...
Hosting Model: https://experienceleague.adobe.com/docs/campaign-classic/using/installing-campaign-classic/architect...
Hope this helps,
Thanks
Denis
