When some users connect to our company via our VPN their DNS doesn?t get changed to resolve to our internal DNS server.
Normally, outside the firewall a ping to mailserver.ourcompany.com will resolve to 206.x.y.z our public IP mx record. Inside the firewall a ping to mailserver.ourcompany.com will resolve to 192.168.x.y our mail servers private IP. VPN users usually once connected should resolve a ping to mailserver or mailserver.ourcompany.com to 192.168.x.y and not to 206.x.y.z. Unfortunately, VPN some connection resolve to the external (public) IP instead of the internal (private) IP. When this happens Outlook is not able to work.
What?s really weird is that this only happens on a few users/systems. Most of the time it works fine.