More Americans than ever are using portable devices to keep tabs on their email 24 hours a day from bedrooms, cars, bathrooms and even church.

AOL and Opinion Research Corporation conducted online surveys with 4,025 respondents aged 13 and over in 20 US cities to measure email usage.

The results suggest that email use on portable devices has nearly doubled since 2004, and that people are checking email around the clock as a result.

The average email user checks their mail about five times a day, and 59 per cent of those with portable devices check their email every time a new message arrives.

Some 43 per cent of users with mobile email keep the device nearby when they are sleeping to listen for incoming mail.

"Email is becoming more and more accessible, and people continue to take advantage of that," said Regina Lewis, consumer advisor at AOL Online.

"As the survey shows, portable devices, like email itself, are becoming more prevalent and easier to use.

"Because users can access email services from virtually anywhere and on almost any wireless device, it is easier to stay connected to work, home, family and friends through email and IM than any other form of communication."

With or without portable devices, 15 per cent of Americans describe themselves as 'addicted to email', and many are even planning their holidays with email access in mind.

About four in 10 email users indicated that it is 'very' or 'somewhat' important to think about email accessibility when they plan a holiday, and 83 per cent admit to checking their mail once a day while on holiday.

Washington DC emerged as the most 'email addicted' city in the US, with 82 per cent of citizens having multiple email accounts, the highest percentage of any city in the survey.

Rounding out the top 10 cities addicted to email are Atlanta, New York, San Francisco, Houston, Los Angeles, Seattle, Orlando, Denver and Miami.

Americans are also emailing anywhere and everywhere. Nearly 60 per cent of people emailing from portable devices check email in bed while in their pyjamas, 53 per cent in the bathroom, 37 per cent while driving and 12 per cent while in church.