per https://doc.dovecot.org/configuration_manual/authentication/sql/, you can add more than one "host=" parameter in the "connect" directive, and leave dovecot to do round-robin load balancing.  there will probably be a delay in processing while a failed database connection attempt times out.

or you can use a load balanced database footprint, using something like haproxy.  its not as simple as putting multiple databases behind haproxy and calling it done.  i use mariadb, which via galera, can do multi-primary HA, where all 3 primary instances can take write or read events.  you need to configure each mariadb instance with galara replication and then setup haproxy to properly attach to the databases and perform a service check.

postgresql or other databases may require different mechanisms to achieve fault tolerant HA.

On 30. Aug 2022, at 5.13, Jack Snodgrass <jack@mylinuxguy.net> wrote:

I am using this file:

dovecot-sql.conf.ext

and in there  I have a

connect = "host=<dbserver> dbname=<dbname> user=<dbuser> password=<dbpass>"

My <dbserver> was down and I lost mail access for a few days before I realized that there was an issue.  How can I specify a backup server so that if my primary sql server goes down, a backup sql server will be queried?

Use haproxy.

Sami