How often do you send reminders to people saying “don’t forget x”, “remember y”? There’s some suggestion that our subconscious doesn’t hear the negative “don’t”, so doesn’t retain the following information.
I haven’t found research that shows this (do let me know if you find some!) but I have noticed that people respond better to a positively framed reminder – “Remember the school fair is on tonight!”
Give it a try in your writing and emails – drop the “don’t forget”, and try “remember”.