Laravel messages email notification

I need to set up email notifications for a messaging system (Laravel/vue/vuex/Pusher).

I already have in app real time notifications, but I´d like to send an email to the users in the conversation if they have not seen the new messages after X minutes.

The trouble I am having is with the logic to not flood the users inbox since I do not want to send an email for every message and I also do not want to keep emailing him about previous messages.

What would be the best way to keep track of what messages I have already emailed the user about?

via Chebli Mohamed