Prompt user to update their email

Hello!

I’m using a combination of WordPress+Buddypress+bbPress.
It used to be a PHP-Nuke website, that we imported everything into a combination of the mentioned platforms and works fine.
Our problem is that since our website userlist is quite old (year 2000), we’ve got over 200k users right now. A lot of those users, used to enter, but maybe now they’re gone or even their email address is not valid.

I’ve been trying to find a way to prompt users that log in, to update and verify their email address, to make sure that users are still valid. I’ve been looking for a plugin that could do this. No success so far.
The idea is simple. All users, should be prompt to check if their email address is valid every now and then (maybe 365 days). This way we would know that users are still using their current email address.

Since people use their username to login to wordpress, a lot of them they forget about the email they’ve got linked to the account.

Well, is there any way to do this at all? A plugin that I’ve missed? Any help will be much appreciated.

Anyway, thank you for your support.