Calendar invites not being sent

Hi there, I have been trying to test out if I can switch my calendar over to mailbox but every time I try to add an email to a calendar event, the event invite is never received by the recipient. I have tried with both proton mail and google, so it makes me think it is something on this end. I cannot find any way to make sure that the calendar invites are actually being sent. Is there something that I am missing? Thanks in advance!