Recepient in appointment does not get an invite

I have em client configured with icloud, use it for contacts and calendar and in addition an imap mail.
If I create a new calendar entry and invite a recepient, the recepient never gets and e-mail with the invite or any other notification to acept, decline the meeting.
Thanks in advance!

Is this with all recipients, or just some?

with all ones, it looks like no invite is sent at all. and I have added the calenda in the account settings of my imap mail

As the invitation is sent by the calendar server (iCloud) could you maybe contact them and ask for assistance?

I do not think they will help as with native mac apps, and outlook 2016 with icloud connector both works fine.
can you confirm that a message shall be sent out once I save and close the appointment, sent from the default mail account, even it is imap?

The invitation is sent from the iCloud server, not eM Client.

If you want eM Client to send the invitation, then create the event in Local Folders, not the iCloud calendar.