BT and Demon Internet are among the broadband providers that offer the most protection from spam to consumers, according to new research.
The study by Return Path analysed non-delivered rates for email promotions and revealed that the inboxes of BT, Demon, AOL and Orange customers were the toughest to get into.
However, Margaret Farmakis, Senior Director of Response Consulting for Return Path, said the issue could have a negative impact on legitimate marketers.
"Internet services providers (ISPs) work extremely hard to protect their customers from the scourge of spam emails," she explained.
"The problem for marketers is that legitimate permission-based emails are often misidentified as spam by ISPs, and subsequently directed to the spam folder or vanish into the ether."
Recognition for BT's anti-spam efforts has come after the company launched its Infinity fibre optic broadband service.
Connection speeds of up to 40Mb are available through the new platform.