I have a situation with a 2930 and two wan connections. One is ethernet, the other is a bridged ADSL.

Due to different ISP's the SMTP traffic has to go via the ADSL connection.

The load balancing rules only seem to operate as a preference, and if the DSL link fails, the SMTP gets routed to the ethernet wan and bounce backs occur.

Someone mentioned static route for the net block of the ISP, or a list of ISP mail server address range.
The drayteks config for static routes requires not only the wan interface, but a gateway IP.
Would this be the static IP we get from the ADSL bridge? also, what happens if the ADSL has a dynamic IP?

I'm just about to install my first dual WAN solution using 2820 routers and wanted to ask the same question about different smtp servers.

I've just had this battle.
If both WANs are on all the time (and why wouldn't they be if they are unlimited ADSLs), the Vigor2820 will use WAN2 for all outgoing traffic simply because this WAN is always up first. This is because the Vigor100 on it is keeping the port live. Then if your client server or PCs are trying to talk to the SMTP server of the other ISP (i.e. WAN1) then you're just going to get errors.
One way around it is to ask your ISPs if one of them can give you SSL access to their SMTP server. As this is authenticated, you can access it from anyway (i.e. the other ISP). I solved it that way. Just had to reconfigure the client's Outlooks and a fix in their Avast antivirus to stop it blocking the traffic and they were away.

However, I've since had this solution from SEG tech support:

"Vigor2820 can router SMTP traffic through the specific WAN interface
you want.
Go to WAN - Load balance policy. Click on Index number to setup the
load balance policy. It can be defined based on the Source address,
destination address and the Service type."

yes but i'm sure that will only work if both wans are up.
when wan1 goes down, all traffic will go through wan2 which is what you want really.
now picture this (for mail servers only)
say a user is using ntl or something similar with a dynamic ip address as a backup. the rdns for that mail server will probably not be correct and spam filters & aol etc will bounce the mail, probably just for the fact of it being from a dynamic range.
the only true way to do it is to have the 2nd wan from a static range with the rdns entries setup.
you could use a smart host for the 2nd wan and setup routing costs to it for the second wan. i know how to do it through exchange but not sure about postfix etc.

sorry, was thinking the user had an on site smtp server there!
maybe, they would be better using a hosting company which doesn't limit smtp traffic to their own network?

Thanks for the info, I too contacted SEG, and they advised that the Vigor can't really force traffic into just one WAN or drop the packets if that wan is unavailable. It will always attempt the 2nd WAN if the first is down.

I got lucky with this install, as the 2nd WAN refuses the connection, forcing it to queue on the exchange server waiting for the correct WAN to become active.
Although the issue is solved, I would still like some info on how to use the Static route function