Tested in Debian 8 / Postfix 2.11
In a environment with Postfix and Mysql as backend, if you have several mysql servers in replication mode (cluster, master-master, master-slave …), you can configure postfix to connect to these servers, so if one of them falls, postfix will try to connect the next available one.
This is made in the configuration file of the mysql connection, in the hosts parameter:
~ $ cd /etc/postfix ~ $ cat mysql-users.cf user = mysql-user password = mysql-password dbname = mysql-db table = users hosts = server1 server2 server3 query = select maildir from users where username='%s'
If you have configuration files for alias, domains, or more, you will have to make changes in these files too.