Email All Users & general sending mails from the server doesn't work

Hello dear users,

my problem is that the server itself does not send any mails. Whether I do a circular email (Email All Users) or when I install a program via script. I do not receive any mails. On the other hand, if I have created a regular mail, I can send and receive mails from there.

I have already checked the DNS-records and everything is connected, otherwise the "regular" email would not work.

Maybe someone had a similar problem where he can help me?

With kind regards,
Tom