Easy way to replicate maildir folders on two servers?

I have two Freebsd servers.

The old one which needs to be rebuilt is a Soekris Net5501 which is in the cupboard under the stairs in my house, sitting on a residential broadband line and using dynamic DNS.

The newer one is in a data centre with a fixed IP address and runs FreeBSD 9.3.

Both are running postfix, postgrey and dovecot.

The people who use the servers are family members running thunderbird clients with imaps.

I would quite like to have all Internet traffic for two domains delivered to the one in the data centre (that's the easy part) but then I would like the maildir folders for either all or selected users to be replicated onto the server in the house.

I would like the imaps client to give exactly the same result whichever server it is pointed at.

This would give some redundancy in case a server ever goes pop, and for clients in the house would reduce Internet traffic.

Should I just rsync the folders between the two servers with a regular cron job, or is there a more intelligent way to do this?