[Dovecot] Migration from Courier to Dovecot: is it recommended to "force" d.index* creation?

[Sandro Tosi]

Hello,
we are planning to migrate from Courier to Dovecot.

We already know courier-dovecot-migrate.pl, that will convert UID list 
and subscriptions files to dovecot format, and we will run it in batch 
on all Maildir + enable it at login, once we do the switch

But we are also wondering it it might be wise to "force" the creation of 
dovecot.index{,.cache} files at conversion-time. It seems that, at 
least, d.i.c is created at FETCH of a mail, i.e. reading it, but we do 
not want to "alter" mails status of our clients.

Is there a way to create them in batch, or is it better to just let them 
be created once clients start accessing their mailboxes via dovecot?

Thanks in advance,
Sandro