CalDav exists, I have looked at it and decided it was not worth the effort (yet) to install software that implements CalDAV protocol, when compared to what I do:
- I enable WebDAV module on apache 2
- Clients use Thunderbird with "Lightning" extension or "Sunbird". Basically the same software but one is an extension to thunderbird and the other is a standalone app.
- Cients use a "Network Calendar" in Thunderbird that points to "http://my.server.com/WebDav/Username.ics"
voila, quick and easy.
We are a very small company, and that works for me, (we have about 10 "online calendars") but I couldn't imagine doing this in a large org without some sort of directory integration or autimatic configure scripts or something like that.
It is nice for the users to be able to access their calendar anywhere where they have HTTP access :-)
I followed some guides that were for ubuntu, although I don't use ubuntu, all concepts are the same. Google will yield short but usefult "quick guides" for this.
In the other respects, I do as you do (postfix for MTA, dovecot for IMAPs, etc etc)