[exim] Regarding spaming from the server

Hi All,

One of my server affected by spammers the using a login id and password one
of mys user and sending mail via other mail ids. for example if my domain
is example.comthey user auth id test@??? and the send mails from
random ids like abc@???, xyz@???@example.com
I got frustated please any one help me get out of this.

Thank you in advance.