Modify mail address of inviting person in calendar

Hi,

we are hositing a caldav server in or network (radiacal).
Setting up the server has required to use a .local domain for the server in out local network.
The user have to sign in with username@xxxx.local.
This is then used as the reply address in the calendar when sending an invitation.
It the recipient then is going to accept the invitation I get an error that the address is not a valid mail address.

Is it possible to set the address of the sender an invitation somewhere so that it does not use the address of the inviting person?

Thanks a lit in advance.

Kind regards,
Wolf