Zammad on other ticket systems => notifications

Hello I would like to use Zammad within the company for the tickets inside and outside to external ones.

What I want to test right now is how can I connect the external ticket systems without them constantly spamming themselves with notifications?

The good thing is that we have fixed e-mail addresses for the external ones and some also have our own mailboxes. Nevertheless, I think that the mutual notification will be the problem or what do you think how could this be solved?