How to send invitation from caldav calendar?

Maybe I’m to stupid, since I did not found any comment on this, while assuming, this can’t be a rarely used feature…
I’m using caldav calendar, hosted on Synology NAS with owncloud. Works fine.
Now want to create event with inviting people. I can add people from my carddav addressbook, no problem. But, also no use, since those people won’t receive anything. How should they, I did not setup any email address to be used for that. In Thunderbird there’s an option to connect a calendar with an email address, which is then used to send the invitations and receive replies. In eM Client I can’t find something ike that.
Any idea?
B.t.w., using any part of Google & Co. is NOT an option. (I wonder, why it is for some people, however ;-))

Hi, unless your CalDav account does not support advanced scheduling, you unfortunately need to have an email account setup in the application in order to send out invites from this calendar.

Thank you,