I was looking for this too. I have having issues with some notifications and subscriptions not sending to certain users while others receive them and it is frustrating trying to figure this out without some type of log of sent emails. I cannot say 100% that the email was sent to the user and it is not in their inbox anywhere(not spam, not anywhere) so I am at a loss as to why this is happening.
I would say to go to UserVoice and submit this but it was submitted in 2011 and even has a response from Quick Base staff in 2018 that says it is being prioritized, the priority may have been low because I don't believe we have this functionality yet. Not much more that can be done if the staff has already verified it and said it they are working on it, just wait. Unless something has changed with it or these are available somewhere else.
https://quickbase.uservoice.com/forums/111823-quick-base-product-feedback/suggestions/1903985-email-log
