As a Cox customer, I was recently notified that I'd have to migrate "soon" to Yahoo for email. (They haven't defined "soon", unfortunately). Cox does provide instructions on what you need to do if you want to continue using your Cox email address with Yahoo mail. I've reviewed them, and honestly think there are a LOT of users who will be unable to successfully navigate the migration. I'm hoping that my "forced" migration happens late enough so the bugs are worked out and the instructions are updated (but not holding my breath).
Regarding woodmeister50's comment that pretty much any email service can be added to the Apple Mail app...this is absolutely true. But keeping the ability to use our Cox email addresses with Yahoo Mail requires quite a bit of preparation beforehand.
To me, this is a blatent money grab from Cox, as I'm not aware of any of the other major ISP's doing this. And from what I've read, this migration to Yahoo comes with ads in our email....unless, of course, we agree to pay Yahoo $5/month for ad-free service.
For me, I'll hold off as long as I can, but am fairly certain this will not be a smooth transition.