First of all, the network setup. We have two offices in separate towns. In the HQ, we have 2 ADSL lines connected to a Watchguard Firebox X550e. The internal network is on a 192.168.16.0/24 range.
In the branch office, we have 2 ADSL lines connected to a Draytek 3300V+ load balancer. This network is on a 10.0.0.0/24 range.
There is a VPN in place between the two offices.
The HQ has SBS 2003 running, and the branch office is using Outlook 2003.
Here's the issue. Using Outlook 2003 in the branch office, when users try to send an email with an attachment, the email either takes a long time to send, or times out with Outlook saying it's lost connection then has reconnected etc....
To test the problem further, I've used a web browser to connect to the Exchange server and send an email, and here are the results:-
The attachment is a PDF of 3.81MB in size.
When I'm connected to the exchange server using the internal server name (whether fully qualified or not) or it's internal IP address, when I click the button to attach the file the status bar sits with the "Sending request to ip address or server name" message for 6 minutes before the file shows as attached. Obviously, this traffic should be going through the VPN tunnel.
However, if I perform the same action, but this time in the browsers address bar use the external ip so that the traffic doesn't get router through the tunnel, then it takes around just 25-30 seconds to attach the same 3.81MB attachment.
Users in the HQ don't have any issues using Outlook.
I need to resolve this issue so that users can use the Outlook client properly and not have issues with it timing out...