Hi folks I'm having the same issue on my iphone 15 pro max. I've been through to virgin and they are giving m the run around and trying to charge me to speak to the gadget team! They say it's not their fault!
They made me change my password and try it again and I'm getting the error message username and password for smtp.ntlworld.com is incorrect. I did try changing the settings to the smtp.virginmedia.com but I still got exactly the same message.
I also have a separate virgin media email account and that sends and receives just fine.
I can still receive my NTLworld emails just it's just sending them that is the issue.
Has anyone found a solution for this please?