To check on the email status of an individual guest, go to Guest list > search by name or email > Last Action.
To check the email status for multiple guests, go to Event Reporting > Reports > Email Deliverability Report. Generating and downloading the report will show delivered status and if a guest has opened the invitation.
Not all guests will have information listed under Last Action. Some email clients and email providers block, or allow users to block, this information from being sent back to the sender.