The SME Server (formerly E-Smith) normally rejects attempt to send mail outside of its own domain if you are connecting from somewhere other than the local lan. This is correct behaviour; otherwise anyone could use your server as a mail relay and you'd become an inadvertent spammer rather quickly.
However, sometimes you have subnets or vpn's that you do want to allow access to. SME Server allows that: you simply use the Administrative browser and add the appropriate network ip's to the Local Networks section. For a vpn connection, that would usually be the private ip address range used such as 10.x.x.x or 192.168.x.x
But VPN's create another problem if they are running over the public internet. The people at the other end will have a routing table that might look something like this:
Destination Gateway default 10.0.0.2 192.168.3.0 192.168.2.1 (your internal network is 192.168.3.0)
If their Outlook is set to access "mail.xyz.com", that's going to route through the internet. The access won't be from the 192.168.2.0 network that you said was OK, it will be from the public internet.
The solution is simple: have their Outlook use your internal address. If your server is at 192.168.3.1, that's what they'd put in Outlook. That access will route through the VPN, and all will be well.
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More Articles by Tony Lawrence © 2012-07-13 Tony Lawrence
After establishing competence and ability, your customer wants to know that you are honest and that you care about their needs. Sell that, because that's what they really want to buy. (Tony Lawrence)