var sidebar_align = 'right';
var content_container_margin = parseInt('290px');
var sidebar_width = parseInt('270px');
Someone tries to send an email to my client account and get this error: "Network Error during host resolution", everyone else send to him no problem. What is the problem here?
Is your client's mail server behind some firewall.
If it is, it could be the reason for the error. Also try a dnsreport.com for your client domain and make sure everything comes up perfectly.