In the image gallery, you can only specify where should be stored all your images.
It can be our default Stripo storage or your own (Amazon, Azure or Other storage).
If you want to choose Other storage your server should support 4 types of requests which you will find in our documentation - GET LIST OF FILES, UPLOAD FILE TO STORAGE, DELETE/REMOVE FILE FROM STORAGE, GET FILE INFO.
Please notice that the DELETE/REMOVE FILE FROM STORAGE request will be used only for systems images (for example when the banner block is generating the new picture).
So if your customer clicks to delete the image in the library for the editor it will be like a sign to hide it. So in general the image won't be removed from the storage (because it can be used before in other emails) but your customer won't see it.
To send this request the Plugin should be connected with your server with Basic Authentication which you should specify correctly (Login, Password and API URL)