Many emailers don't realise that web-based providers are scanning their messages in order to provide relevant advertising.
A survey conducted by email service GMX found that 40 per cent of people did not realise that it was common practice among some email providers to scan messages for the purposes of targeted advertising.
GMX found that many people questioned relied on web-based, free email services and around a third thought they should be able to opt out of such scanning.
Only two per cent thought the practice was in their best interest.
Eva Heil, managing director of GMX said: "It is understandable that many Britons are wary about their private emails being scanned for advertising reasons.
"It is certainly important that every user is at least informed if this is done by their email service," Heil continued.
Google uses targeted advertising in its Google Mail service, though a similar scheme operated by a company called Phorm, based around surfing activity rather than keywords in email, has attracted a great deal of controversy recently.
www.gmx.co.uk http://mail.google.com