There are a couple of things you would need to do.
- Open your router to allow calendar traffic in and out of your network (be carefull about opeing any custom ports on a router as it could allow for unotherised attacks). All internal user passwords should then be strong and all traffic should be encrypted.
- Have your external server.mydomain.com DNS point to a public ip address. - At your router you can rout it to the server machine (public ip's would be supplied by your ISP). This will allow external calendar subscription traffic know where to get the information from.
- For invetation replies to work from outside your network to your internal network you will need to get your ISP to set up reverse pointer for your domain to point to your public ip address. This allows people outside your network to accept or decline your calendar invetation - and allows your calendar server to automatlycally post those replies in the relevent calendar.
I havnt gone into much depth with these steps because personally I have moved to using iCloud.
For all the hassle and potential risks of opening up your network I would alternativly set your users up with a free iCloud account and use the calendar service there. Super easy and it works. It also limits the potential external attacks on your network.
Thanks for the suggestion, but that's not what I'm looking to do. All networking setup is in place so that invitation functions are already working. I'm looking to publish an entire calendar to a public place so that people can subscribe to it via its .ics file, but without using iCloud. I'd like to do this with our own server. While this functionality works for calendars that are "On my Mac" it is not an apparent feature for calendars that are hosted on via the Calendar server. Looking for a work around, as some sleuthing has allowed me to uncover the calendar's URL.
Has anyone worked around this before?