Millions of legitimate emails getting blocked by ISPs

As the war against spam heats up, internet service providers (ISPs) are blocking millions of legitimate emails every day.

The worst hit are social networks. More than a quarter (27 per cent) of Friends Reunited's emails, for example, were bulk blocked by ISPs in May, according to email delivery company Return Path.

"About one in five commercial permission-based emails are being blocked globally, and 15 per cent in Europe are blocked because ISPs are treating them as spam," Margaret Farmakis, senior director of response consulting for Return Path, told sister title PC Pro. "I wouldn't be able to say if it was millions or billions, but it is countless."

"We're not talking about spam, these are emails that people have asked to receive, but that are being treated like spam," she added. "It doesn't effect one-to-one emails, but a lot of marketing emails and communications from social networks, for example, are never delivered to the end user."

According to Return Path, email is often caught in the spam trap because some end users flag emails as unsolicited when actually they have just got bored of receiving emails from a company. If a company receives too many spam reports around one per cent of mails from any one company then all emails from that company are tarred with the same brush.

Social networks are increasingly falling into ISPs' spam filters because of the way subscribers sign up to the services, with networks often suggesting that users import email address books.

Return Path said emails from social networks were twice as likely to be caught up in the ISP bulking traps than mails from other industries.

"The practice of importing loads of addresses can have an impact," said Farmakis. "Effectively you are sending a lot of emails to people who haven't asked for them, and some of those email addresses could be really old, which might be out of use or being used as spam traps. It can be risky."

Despite the high number of false positives, Farmakis refused to blame ISPs for the wrongly blocked missives, saying that some legitimate emails were inevitably going to be caught in the crossfire.

"Between 97 per cent and 98 per cent of all email is spam," she said. "ISPs have to weed through it and try and discover what they should deliver and when they should protect their end users from spam. It's like they're fishing and if a company's email looks too much like spam they get caught up in the net."