"With personalised internet marketing, every response and transaction can be measured - from customer and lead acquisition to customer satisfaction," said Duffy, speaking at the Emarketing for the Internet Age seminar in London recently.

Email remains crucial for online campaigns because it's the only push technology firms can use, according to Duffy, of Boston's Northeastern University.

"Everything else on the internet is pull. The only way to stay in touch with customers after they have opted in, is by email. Web marketing will only expand as the pipelines to target audiences get wider."

Electronic marketing tools application service provider Marketfirst, sponsor of the event, claims internet service provider Verizon and GE Plastics have increased response rates with targeted emails.

Verizon was losing 30 per cent of its customers after a free month's trial offer of its services, but cut this by half in 30 days. It introduced a personalised email on a weekly basis for the offer month, containing hints for new subscribers, says Marketfirst.

GE Plastics, with a UK-hosted system, saw increased response rates of between 30 and 40 per cent.

Almost nine out of 10 retailers use email marketing, and find it more effective than methods such as banner and print advertising, says Forrester Research.

"Email's efficiency will plant customer retention at the centre of the marketing universe," said Jim Nail, senior analyst at Forrester, which studied European retailers.

"The technologies that allow email personalisation will transform marketing's perspective from viewing customers as targets, to valuing them as resources to be nurtured," he added.