Is it a list of trash mail addresses by default or is there an assumption that people made trash mail addresses specifically for the app? If it’s the latter, I

Is it a list of trash mail addresses by default or is there an assumption that people made trash mail addresses specifically for the app? If it’s the latter, I suspect that won’t happen in practice for the majority of users. I haven’t heard of threema, I guess users have to share their IDs manually with each other in that case?