Virgin Media customers with @ntlworld.com email addresses are rejecting most emails as Spam after a messed up migration of their mail servers. Most of these mails are being completely killed with no bounce-back to the sender and they are not going into customers' spam folders. NTL world mail hosting was provided by Gmail service for ISPs until that was ended in July and Virgin moved @ntlworld.com email account customers to an internally hosted solution. We noticed a story in The Register today who have reported on numerous Virgin Media customers have been reporting this on customer forums . If you get customers reporting that they are not getting your emails and they use @ntlworld.com email accounts, it might be worth suggesting they use a different email povider. More recently virgin media customers are now reporting that they are receiving floods of spam.

Either  way, your  emails to virgin media customers maybe getting drowned in a spam deluge or not delivered to your customers at all.