Although your guests will have no doubt received your invitation, we cannot 100% guarantee that you’ll be notified that it was delivered or opened.
Spam is the reason email programs disable the mechanisms that could be used to track email reception.
This means your recipient’s right to privacy overrides your need to know if it was delivered or not.
We have no control over your customers’ security settings and in some circumstances they don’t either (when working behind company firewalls).
Creating an online invitation + barcodes & RSVP