Omnichannel - sending emails

in my company we want to start implementing an Omnichannel tool for email management, manuals and marketing campaigns, we also want to use social networks, etc. But I wanted to know and learn about some experience more than anything with sending emails because we particularly need to know not only the email metrics (clicks, openings, rejections, etc.) but also to be able to see the body of that sent email, see the content and its attachments. Of all the tools that I investigated, none of them store emails to be consulted later. Does anyone know of any that do? Or could you tell me how I could approach a development that allows you to store this information? Thank you very much.-