Unable to send mail to created mail accounts

I setup centos web panel. My primary Domain was mapped automatically. I created a user and email accounts to my primary domain. However my primary domain is not listed while navigating to List Domain.

I tried to send email using Roundcube link given in web panel to my one of my domain mail but i am getting following error. I even tried sending from gmail but i did not receive it in my domain inbox.

SMTP Error (450): Failed to add recipient Recipient address rejected: User unknown in local recipient table

How can I fix this and why it is occurring? please help

Thanks

I just fixed this my changing my hostname. earlier my hostname is same as my domain name. After changing the hostname to something like server.<mydomain>.com and i removed $mydomain in $mydestination in /etc/postfix/main.cf

Thanks