ispconfig3: setup a secondary/fall-back mail server
What is the correct/intended way of configuring a secondary/fall-back mail server within ispconfig3?
Especially one that will also start bouncing on non existing accounts/domains and does spam/virus filtering before passing the mail to the primary mail server.
This because till now it seems to cripple the spam efficiency if this bouncing/filtering is only done by the primary mail server receiving the unfiltered mail from the secondary mail server.
Till now I did the following which works fine, but I wonder if there is a cleaner/better way of doing it.
Make the local mysql server on the secudary mail server a slave of the mysql server of the primary mail server. (using SSL, as the replication goes through the public network).
On the secondary mail server there is no need to run the ispconfig cron, as it is not known to ispconfig and there are no ispconfig triggered changes that need to take place on this server.
Make the postfix/spamassasin config on the secondary mail server equal to the primary except for some changes to the transport_maps and forward all accepted mail to the primary mail server on a different port which won't pass the mail again though a spam filter.
In the meantime I see I can also define a mirror server within ispconfig which will get all config changes for mysql too, so I won't need a mysql master/slave setup anymore.
But still I will need to hack the postfix config as mentioned above and will have an ispconfig cron running which will execute unneeded file system changes (like mailboxes) on the secondary mail server.
Maybe I'm missing an obvious way to configure the wanted primary/secondary mail server setup within ispconfig.
Thanks in advance for any suggestions or clarifications.