An error occurred!SMTP Error (553): Failed to add recipient "xxxxx@gmail.com" (5.7.1 sorry, that domain isn't in my list of allowed rcpthosts (chkuser)).
Hostname are
[root@ns ~]# hostname
ns
[root@ns ~]# hostname -f
ns.mywebsite.com
[root@ns ~]# hostname -s
ns
[root@ns ~]#