I have not received an email, but logging in to the account there's a notice now that tells me about the impending changes.

¯\_(ツ)_/¯

It's finally time to migrate away, I've been putting it off, but so far the accounts I created seem to have mostly become dormant, so only one user has to change, and I'll just re-create them an IMAP account for their mail, they don't use any other services.