Meaning of ずにはすまない

I would like to know which is the meaning of the structure ～ずにはすまない.

According to several pages that I’ve found on Google, it means "must, have to" as well as ～なければならない. However, in other websites ～ずにはすまない seems to mean "not having another option than" (like ～ざるを得ない). If ～ずにはすまない means the same as ～なければならない or ～ざるを得ない, I would like to know the difference between these structures.

If besides that, you could please give me an example of ～ずにはすまない I would be really thankful.