[Dovecot] Expire plugin with multiple mail servers

Hello we are running Dovecot 2.1.9 and I want to configure expire plugin. We have 2 proxies with director and 4 mail servers.

I have configured expire plugin on a single mail server and it works Ok. I don't konw how to configure with 4 mail servers and 2 proxies. My first idea is create on each mailserver one sqlite database and configure the expire plugin on proxy, but I don't know if this is a good idea. I don't know if the database should be in one proxy, and I don't know which server has to do the "doveadm expunge" command Do you have any idea how is the best way to configure expire plugin on this scenario?

Thanks in advance.

-- Ramon Frontera Gallardo Universitat de les Illes Balears