Two responses from appointments

Every time I create an appointment in Outlook, everyone I invite gets two email messages about the appointment. Also every time i reply to an appointment (doesn't matter if i accepted or declined) the creator of the appointment also gets two responses.

I suspect this started when I installed "Outlook CalDav syncronizer" to Sync my calendar with my companies local IMAP server, and the change I noticed is that my calendar folder renamed itself from "Calendar (This computer only)" to just "Calendar".

I tried to convert it back to a local calendar (it used to say "This Computer Only") but I cant find a way to do that. I tried transfering the appointments to another calendar and then deleting it but Outlook won't allow it.

Any help would be greatly appreciated 😄

Thanks in advance.