Help! gehackt, need postfix and mail service new installed

Dear Joe,

my server was gehackt, and the hacker has sended many spam mails from my server.

I have changed the server password, and I have changed the setting of postfix server.

Now the postfix server doesn’t function any more.

Can I install the postfix and related service without get my email deleted.

I use the server mainly for email and file storage, it is not in much use.

I need a seperate mail server late and better security measure. But I don’t have time
for the time being.

Many thanks in advance.

Furthermore can I in postfix configure so that no user can send email use other domains.

the hacker has sended email use domain from my server