In this case, doesn't changing the MX record to the main ISPConfig server cause now that server to be the single point of failure? I'm just wondering how this behaves like a backup MX in this case. For instance, we have 2 ISPConfig servers running in multi-server mode ... so www1 is master to www2 but both have different customers on them. I want to make www1 the MX backup for domains on www2 and vice versa so that they back each other up. In this case i would put 2 MX records in for each domain with different priorities ... is the routing the way to do this? or is there some other method in ISPConfig.