NotifyLink Enterprise Server:

Information: There are variations of the behavior of the 'Delete Invitations From Device' setting (User Policy -> Calendar Sync Setting). The following is a list of exceptions and the servers they pertain to:

Communigate Pro
'Delete Invitations From Device' may not seem to work if you respond to the meeting from the Inbox in the CGP webclient. This is due to the fact that the web client does not update the corresponding event in the calendar. If you instead respond to the meeting from the event itself or in Outlook, this issue does not occur.

MDaemon and FirstClass
Because MDaemon and FirstClass don't send invitations to the device, the Delete Invitations From Device setting does not apply.

Scalix
The Delete Invitations From Device setting only applies to invitations that are responded to from the device. If you respond to the invitation on the server, this setting will have no effect.

MeetingMaker
Tentative and declined meeting responses are treated the same as far as the 'Delete Invitations From Device' setting is concerned. In other words, a tentative response will be deleted from the device even if 'Delete Invitations From Device' is set to Only Declined.