I have created a new event page and on the online registration page I have entered the 'Confirm From email' address that I want to use. However, when someone registers for the event the confirmation email is being sent to a different email address that was used for an event in 2018. This alternative email address was listed as disabled on the 'From email addresses' list and I have since deleted it but messages are still being sent to it from this new event page. I can't find anywhere in the CiviCRM system where this email address exists to change or delete this association with the event page. Where can I look to edit or delete this association?
I can think of three possibilities. Let's call the email address that is erroneously receiving these emails the "mystery email address".
Your payment processor is configured with the mystery email address for notification. If this is the answer, then the emails you are getting would be not from CiviCRM and you'll probably be able to see that from the contents.
When creating the event, you copied/cloned the previous event, and the address was somehow carried along in a field that you're no longer seeing.
One of the email addresses that is being notified (correctly) has been configured to automatically forward a copy to the mystery email address.
To further diagnose the issue, take a look at the email headers of one of the emails that you received to the mystery email address. It will show you some details about which address is was originally sent to, as well as where it originated from.