Question : Port Forwarding over Draytek VPN - help needed


I could really do with a bit of help on this one.

The scenario is as follows:

I have a Draytek 2820 on site A and a 2900 router on Site B. The routers are linked through an IPSEC VPN tunnel. The 2900 is set to "dial-in" to the 2820. And the tick at the bottom of the Lan-Lan VPN on the 2900 router is set to direct all traffic through the VPN link and through the 2820.

Site A (2820) has internal IP range of 172.16.12.x,
Site B(2900) has internal IP range of 172.16.200.x,

Now all works ok with traffic from site A to site B and when you browse the web from a machine on site B you go over the VPN to site A and then out through the 2820 router accordingly.

This is my problem:

The MX record for my mail system is to a WAN alias on my 2820 router in site A. I am moving our mail server over to Site B, however I need to find a method of directing all SMTP, POP3, IMAP, etc traffic coming in on the WAN alias of the 2820 across the VPN to Site B and then have the "outbound SMTP" IP address which the mail server on site B responds from be that of the 2820 router.

I have looked at the port forwarding on the 2820 router and it only allows you to port forward on the local network (172.16.12.x), where I need to forwarding to go to 172.16.200.x

Can anyone advise as to how I get the above scenario to work ?

Many thanks

Answer : Port Forwarding over Draytek VPN - help needed

I can help with the SMTP relay.
An easy way would be to install IIS and SMTP (add remove programs > windows components>  onto an XP box at site A or similar.
Open iis though mmc. Right click domains under default smtp virtual server and select new domain and select 'remote' enter the domain eg
Then configure the connectino so double click it and
Tick allow incomming
click formawrd all mail to the smart host and enter [172.16.20.x] where x is the local ip.
staart the smtp (simple mail transfer protocol service through services

Point the port 25 on the draytek at site A to the xp box on site a. On the xp box setup a smtp relay that points to the mail server at site B. This will allow email directiion until the MX records are updated.  The Xp box would also 'hold' the emails while the mail server is moved form one site to the other,

Otherwise get a dynamic dns host name (, point your company mx records to that. Then change it once the mail server is at the new address.
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