Is there some kind of "web-part" way of working with Newsletter email templates?

Hello,

We're making a newsletter templates where we need to have some sort of way to add blocks with content. The only thing we found was the placeholders, where we can write text or macros. But we need the next level. Pre-made blocks, like a form of transformations that can be filled when making the newsletter.

Does this exist? If yes, where can i find it?