speed up doveadm search

[Vu Ngoc VU]

Hello, I have recently migrated our mail accounts from old setup with courier-imapd to Dovecot 2.

I thought that I can search quicky messages in mailboxes with doveadm because of indexes.

Our users are asking (sometimes) to remove messages that they have sent wrongly. Some of them are coming from Exchange, and there is a feature in Outlook to recall (to delete) a message.

So basically, they give me some infos (date, sender, subject) of message to remove.
And I planned to do "doveadm search", then "doveadm fetch" and at last "doveadm expunge" on the found results.

But it appears that the first run of doveadm is very slow. I don't know if it is because some indexes/caches are missing at this time. But when I run again same commands it is fast.

Could you tell me if I speed up search on our maildir storage?

I have no idea if I must manually (or with cron) run "doveadm index" on all our accounts because index/cache is only generated when users access their mailboxes.

Or do I have to tune some settings like : mail_always_cache_fields, mail_cache_fields, mail_cache_min_mail_count, mail_never_cache_fields

Thanks