Virgin Media said "no further emails are able to be sent in this manner" after some of its customers complained they were being spammed following a group email.
A Virgin Media spokesperson said:
A small proportion of our customers have received an email from one of our suppliers which, if they reply-all, it is sent to a wider group.
We’re investigating exactly what has happened ... We apologise for the inconvenience caused.
More top news
A giant panda has been caught in camera breaking iron bars and moving into the other cell to have a taste of milk in the next cell.
City traders are paying up to £200 to cure their hangovers with a vitamin drip, according to a doctor from Surrey.
Serena Williams won her sixth Australian Open title with a hard fought 6-3, 7-6 (7-5) victory over Maria Sharapova in Melbourne