But what I will need to happen is that all the email servers will need to share the one mysql database.
By doing this they would basically be in a mysql master-master relationship.
Thats the wrong way to set this up for ispconfig. ISPConfig uses its own replication mechanism.
The ISPConfig setup must be:
1) Create the master server. Make sure that the directory /var/vmail is on a shared medium that all servers can access e.g. a cluster filesystem like glusterfs or a SAN or a NFS server.
2) Create as many slave servers as you need. the /var/vmail directory must be the same shared network drive that you used on the master server. Ispconfig has to be installed on these servers in expert mode, select yes when the installer asks if you want to join a mster server. Select 'n' when you were asked to install the ispconfig interface on the slaves.
3) Login to ispconfig on the master server, go to the server settings and edit the settings for every slave server and select the master server in the "Is mirror of" option field and select save. Ispconfig will then replicate all email user settings to all slave servers automatically.