We offer email hosting with a product that uses postfix. We use the sender_dependent_relayhost_maps configuration to relay outbound mail for some of our users through a 3rd party smtp server.

Everything is working fine but we were wondering if it is possible to list multiple ips for the relayhost, for fallback servers.

The configuration is in a text file which looks like:

whateverdomain.com [XXX.XXX.X.XXX]

Google didn't help me much with this one. We're using postfix 2.6.6