First of all: I read very carefully through what @Stefano_Zamboni wrote.
Maybe I don't get it, but sorry, maybe you are misunderstanding but that has nothing to do with forcing someone anywhere. Not even a mail-server no matter how much you turn it is not a piece of interchangeable thing, it is an application. Let me ask this way: If you use a MySQL database, can you just with removing it and installing PostgreSQL run the data from the MySQL? No! It's simply an application that has a certain data storage format.
As I pointed out earlier, also with Dovecot you have mbox, Maildir, CyDir, dbox and even dovecot does not support all "standard"-formats such as mailstore or mbx.
The reality is: If you have a different format, you have to do a migration. That is exactly the same case with a dovecot from another mail server for example or from a format which dovecot does not support, such as mailstore for example. There is no difference what Kopano does. We have MAPI as a storage format, and since we are the only open source MAPI backend we have this specific type of storage. Even if we wanted to: Maildir or any of the above storage formats are not capable of storing the metadata MAPI can, so yes: You have to migrate. This has nothing to do with forcing someone in a certain format, sorry.
Sure, It's not nice you would need to do a migration, but simply: If you don't need/want Kopano: Perfectly fine! Fortunately, we live in a great world with freedom of choice. If you don't like Kopano? Just use the migration scripts we provide (also away from Kopano). You won't have all the extensive feature-set then, but if you don't need it then Kopano is maybe something you simply don't need at all - and you still get the data you had in Kopano. Don't get me wrong, and I'd love to live in a world with one "storage-format-to-rule-them-all". But I believe you are asking for the impossible.
Let me give you an example: There are no contacts, notes, tasks, calendars, files in IMAP. How should you then be interfacing them with something else then? At last, let me give you this example the other way round: Please uninstall roundcube with the calendar plugin and install anything else with calendar support. I don't know any other solution which can work with that format - Wouldn't that also be "Forced" based on your definition?
Please realize: Kopano is not a mail-server, it's much more. If you want a plain mail-server with nothing ontop, dovecot is CERTAINLY a better choice.
So after all as for RPMs: https://download.kopano.io/community/ - Use it if you like it, leave it if you don't.