iCal server, problem with mail options

Hi, please help. I have OS X Yosemite 10.10.2 and Server Version 4.0.3.

I have a two questions:

1.

What should I do to all domain users and calendar users received an invitation by the mail?

Now invitation by the mail get only external users.

2.

When external users get invitation by the mail, they can not answer the invitation initiator, because address for a response ical+6358c658-2db1-4af5-9649-41cc711e8ad6@ical.int and this address is constantly changing. What should I do to change this parameter?

Kind Regards, Pavel.