Multiple Email Routing for the same domain
I successfuly used email routing/relay recipient to create a relay server for my customers with a internal mail server.
In some case, they have 2 Internet connections (a primary and a backup) with 2 different IP addresses, and a cisco router which is able to open the backup connection if the primary is down; in this situation the mail server is accessible from external using the backup IP Address and I have to manually modify the email routing destination address in ISPConfig.
I see a "sort by" field in email routing configuration: it seems like "priority" for DNS MX record: then I tried to configure a second routing server with the same domain but with different priority... but I recived an "domain_error_unique".
Now the question is: what is "sort by" field?
Can I configure a backup email routing server for a domain?