We have an equipment mailbox in our organization. We use the calendar of that mailbox to share important events.
For my own calendar, I can publish it and receive an ICS link, which I can then use in other applications. However, I can not do that for the equipment mailbox calendar (the option is disabled).
How can I make this calendar publicly available? Proof of concept would be importing the calendar into Google Calendar.
The Exchange mailbox is nothing else as an taskuser. So you could come up with a 3rd party software which sync the calendar from this taskuser into the google cloud (as the Outlook client sync will only happen when outlook is up and running). However as this isn´t what companies normally like (due to the reason that private data might left the company) you would have problems to find a 3rd party software (e.g. maybe Sync2 Cloud might work for you) which might offer exactly that out of the box.
You also could start to build something fully on your own (use Microsoft Exchange Web services) and push that information overt to google calendar.
According to MS Office 365 support, this is simply not supported.
Calendar publishing is only available to licensed user mailboxes.