hi Olivia,
I would suggest you state in your email that you need the user's explicit Consent for you to be able to keep communicating with them after May 25. I think that gives it more weight, clarity and urgency than asking them to update their profile. My 2 cents :-).
I agree with Sanford. I would also have the opt in acknowledge and agree to a linked privacy policy, so you clearly have full data processing consent as well.