How to separate mailboxes on storage fs?

[sabinich]

Hello!
I've read documentation but don't understand one thing: how to separate mailboxes on storage fs?
When I've been checking two email-accounts on different domains, every mail stored into one default message folder.

[Chris-Scot]

I can do this
sql local_mailboxes {
imap_filter command /var/lib/maddy/filters/{account_name}.sh
}
Or this.
imap_filter command /etc/maddy/sieve.sh {account_name}

So why can't I do this?
storage.imapsql {
driver sqlite3
dsn imapsql.db
msg_store fs messages/{account_name}/
}