I know this has probably been done to death, but searching hasn't helped get answers...
My partner has had an @btinternet.com email for (she thinks) around 20 years, she is certain that she has had it for so long it might even have been @btopenworld once which makes me think it started with very early broadband but she thinks its way before that, that she's had BT email of some sort since mid-late 90s, not even dialup she says she was using it even when her only internet access was net cafes etc... I mentioned LineOne
I have always had my own domain etc... so not an issue for me.
I heard somewhere that certain 'ancient' 😉 BT email users actually had permanent free accounts not tied to a broadband package... Is there any way to tell? Will BT still invite us to Premium mail even if, technically, we wouldn't have to pay for it? A friend of ours is in the same boat, told her email would cease but still working 3 years after switching to VM (but blimey if it was me I'd not be chancing it...!).
We're finally about to ditch BT, and whilst she has been transferring lots of email to a new gmail address, it's actually quite an eye opener how many people she is registered with where changing an email is not that simple! (Top 3 problems are 'confirmation' emails that never arrive, emails that say they have changed but continue to send out important correspondence to the old address days later, even though the email to login has changed, or simply that when you click 'edit' on the account pages nothing happens, including a huge insurance company - I tried on my account and got the same error...)
At the moment, you either have to be a BTbroadband customer or pay £7.50/m for premium mail. There is no free mail for non broadband customers however long they have had their address.
As has been pointed out, you would need to take out a BT Premium email subscription to keep your email address if you leave BT however this might change in the future.
This link which is available with a search of the Internet "Choose email type BT" would appear to indicate that BT are are going to introduce a free "basic" email to those that are no longer BT customers.
You can also have your BT email account linked to another person's BT Broadband account. You would of course need to have the person's permission and trust them not to delete your email account. They would not have access to the account without knowing the password.