BT have informed me that if I do not log into the bundled email account, it will be closed.
I use this account rarely, but I find it odd that BT would even consider closing the email account of an ongoing customer.
I believe the wording should have been better. Remove the threatening tone and justify it by refreshing login details or just confirm that I still have the credentials.
It could be a scam message, there are a number of them circulating, so do not select any link in the email, as it will result in the compromise of your account.
While it is possible that you have received a scam email, BT do delete email accounts that are not frequently being used.
In any event you should never use any link in any email in order to log onto your email account or any account for that matter as it could very easily be a scam email and by using the link you will have given the scammer the keys to the kingdom.
If you get any emails asking you to verify any accounts do it by logging on directly to the relevant account and not by using any links.