What has happened with old legacy Email Accounts in the past few days? (NTLWorld, BlueYonder)

Like many others here, my old @ntlworld.com email account has stopped working yesterday evening (Thursday 23 October around 7PM).  Android Email app keeps asking for the password.  Works OK on my Windows Outlook.

I've seen a dozen other people raise the same issue, with different combinations of what does and doesn't work - all regarding the legacy email addresses, within the past day or two.

So far, the only solution's I've seen are the "try resetting the password", or "try setting up a new VM/O2 alternative email account" or "try setting up an App Password" -type solutions.  All good suggestions, I'm sure, but they don't address the actual issue.

This appears to be a problem, or a change, on the VM server side.  With so many people raising the same issue at the same time: this doesn't look like a client device or client account-type problem - there's a problem at VM that needs correcting.