Hey,
This is possible, but you shouldn't really leave your customers do that because not all of them will have the knowledge to do so.
Anyway, you can allow customers to add delivery servers, either from backend -> settings -> customers or iof using groups, from the group settings.
Once you do that and your customers add bounce servers, mailwizz will automatically process all the bounces and depending on variuous factors those emails will be blacklisted.
Anyway, please get familiar with the app first, it has plenty options that you have to learn.
Thanks.