Multiple Smart Hosts

Multiple Smart Hosts

Post by Robin Wenh » Tue, 16 Sep 2008 21:11:25

Hi, is it possible to configure multiple smart hosts for back up reasons.
I've found references to using multiple smart hosts, but the references
suggest that this is for load balancing.

I'd like to configure SBS to use the primary ISP's mail relay most of the
time, but if the WAN connection fails and the firewall switches to the
backup ISP then I need to use their mail relay.

I've considered using direct (DNS) delivery, but the backup ISP does not
allow me to configure an rDNS on this link :-( which will have other

Thanks in advance.

Multiple Smart Hosts

Post by Lanwench [ » Tue, 16 Sep 2008 23:45:40

It isn't really possible. I'd probably use a third party for a smarthost
(DynDNS has MailHop Outbound) and use the same one regardless - you
authenticate to it, and it doesn't care what IP block you're coming from.


Multiple Smart Hosts

Post by Cliff Gali » Wed, 17 Sep 2008 02:51:15


As lanwench has indicated, you cannot accomplish what you are trying to do
with SBS. I'd like to know, however, if your ISP has an rDNS entry
configured for your IP. It doesn't matter if they let *you* configure it.
As long as one exists then you can switch to direct delivery without
problems and that would be my recommended solution.


Multiple Smart Hosts

Post by Robin Wenh » Thu, 18 Sep 2008 21:36:15

Hi Cliff

The provider of the backup ADSL does not provide rDNS, which is the root of
the problem.

The primary provider does - which enables us to use DNS delivery most of the
time but as indicated this could lead to problems when we switch to the


Multiple Smart Hosts

Post by Robin Wenh » Thu, 18 Sep 2008 21:38:03

"Lanwench [MVP - Exchange]"

Thanks for the response, Lanwench, that is what I thought.

I'll contact the primary ISP and see if they can provide an authenticating
SMTP relay that can be used from the backup ADSL. Failing that we may
revert to the man-draulic method of simply changing the Smart Host to the
backup ISP when we have a major problem.

Multiple Smart Hosts

Post by Paul Shapi » Sun, 21 Sep 2008 05:37:19

I have the same issue. I don't have a complete automatic fix. But I was at
least able to stop my mail server from sending mail directly on the backup
WAN connection, since much of that mail will be rejected these days. I set
my firewall to only allow smtp on the backup WAN connection to my 3rd party
smarthost. I use DynDNS's Mailhop Outbound that Lanwench mentioned). I
created a second mail connector in Exchange to use that smarthost. So when
the primary WAN fails, I go to Exchange and disable the standard mail
connector and enable my backup connector. I tried setting priorities on the
connectors, but the mail waits in the higher priority standard connector
queue rather than rolling over to the functioning backup connector. So it's
still a manual changeover, but at least I don't lose any outgoing mail.