Hierarchy separator recommendation?

Dear dovecot list,

I'm using Maildir as mailbox format.

Is there any recommendation for the namespace hierarchy separator?

Currently I didn't set any. So it is the default of dot '.'

I'm switiching from a rather unknown IMAP Server called DBMail (http://www.dbmail.org/) Planning to synchronize the mailboxes via imapsync (https://github.com/imapsync/imapsync)

Is there anything I should be thinking / planning about?

Or can i always change this namespace hierarchy separator later on?

Any hints or insights are more than welcome ;)

thanks & greetings Becki