Timo,
We are contemplating building an S3 compatible cluster of storage servers using Pithos <https://github.com/exoscale/pithos> and Cassandra to get multi data center redundancy and availability. Would it be possible to have multiple Dovecot servers in disparate geographical locations all talking to the same object storage, assuming it's consistent between sites? From what I remember about obox the dovecot servers all keep a copy of the index locally and merge it with a file in the object storage at intervals, is this an issue with our concept? Also does your team have any performance analysis data on the obox plugin, or data on it's use in production?