So this is an assemblage of FOSS software, presumably with a bit of custom glue software thrown in. The 5-user limit is if you want FREE-BEER support. It's not

So this is an assemblage of FOSS software, presumably with a bit of custom glue software thrown in. The 5-user limit is if you want FREE-BEER support. It's not very clear. I'd like to know what they used to build it. Postfix, apparently (good choice). I'd like to know what other components they are relying on: Dovecot? Some OSS CALDAV server? Many people have tried to implement a free version of Exchange Server/Outlook. Despite the overall crapness of both MS products, those people have struggled. If these people have managed to do it using COTS FOSS components, I'd like to know what components they are relying on. They don't seem to be offering that information on their website.