Shared folders using mbox format

[Alex]

Hi,

I'd like to create a shared folder to be used with an Outlook client
and a Thunderbird client. We're currently using mboxes.

I've read the documentation here about creating a shared folder:
https://wiki.dovecot.org/SharedMailboxes/Shared

It doesn't make reference to how to do this using mbox format. Is it
possible? Should we convert to Maildir? Perhaps there's a way to
provide both formats?