Hello,
If you want to disable the accept button on receiver side or make them unable to send a response after certain date, you need to develop an add-in and force receivers to install. I dont think this makes sense.
For your requirement. i would suggest you create a rule or add-in to mark the response mailitems as read or delete them.
You may create VBScript or add-in to check the mailitem when their response arrive and loop all appointments in your calendar, if it exceed the deadline, make it as read and delete the item.
How to: Programmatically Perform Actions When an E-Mail Message Is Received
How to: Programmatically Move Items in Outlook
Regards,
Celeste
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