Notification settings

Hello everyone
We use ERP Next as a ticket system in our company. Well, until recently the e-mail notification still worked in our system. Unfortunately, this has not worked for some time now. I have tried every setting. Be it in the
notification settings or even a notification after a certain time without a reply in the e-mail itself. Unfortunately, this is essential for us, as it allows us to respond directly to our tickets.
Can anyone help me further? I am slowly but surely reaching the limit.

Thank you for the answers and tips.