The last 24 hours I've had close to 300 emails put into my spam folder. That is normal.
Amongst those emails two of the senders had used the possibility to ask for a notification when the mail was deleted. This is a smart one that I don't think I've seen before. Maybe once.
Answering yes to the notification question is as bad as trying to unsubscribe from the spammers list. You confirm your existence.
So, look out for this trick. It may be a new trend.