Indeed, the new subscriber notifications must be improved. Especially, I would like to see a differentiation between new and existing subscriptions. Currently, when a user who has already subscribed to one or more lists subscribes to another list, the admin notification mail will show all lists the subscriber is now subscribed to, even deleted lists. When customizing the notification mail, it should be possible to display this info separately – the newly subscribed list and other lists that the user has previously subscribed to.

Yes please

+1 for that

Hey Maey, I think this feature already exists. It's in the MailPoet > Settings > Basic. You do have to turn the feature on and enter the email you would like to receive those notifications.