Webmin System and Server Status email alerts

Hello All,

I am trying to set up email alerts from Webmin for Disk Space. I have added Disk Space from the Add monitor of Type.

Next:- In the Scheduled Monitoring, My configs are as follows:-
Email status report to:- azeem@xyz.com
From: address for email:- admin@xyz.com

But still, I can’t able to receive any email alerts.
So when I am checking from server:- /var/log/maillog, It is showing:- webmin@hostname: Sender address rejected: Domain not found (in reply to RCPT TO command))
And here (webmin@hostname, the hostname is my server name)

Can anyone please help me in setting up the email alerts. And Postfix is also installed in my server.

Thanks & Regards,