Naperville is a city in DuPage and Will counties in the U.S. state of Illinois, and a suburb of Chicago.

Naperville was voted the second-best place to live in the United States by Money magazine in 2006.

It was rated 1st on the list of best cities for early retirement in 2013 by Kiplinger.

In a 2010 study, Naperville was named the wealthiest city in the Midwest and eleventh in the nation with a population over 75,000.

It was ranked among the nation's safest cities by USAToday and Business Insider.

As of the 2010 census, the city had a population of 141,853, which was estimated to have increased to 147,100 by July 2015.

It is the fifth-largest city in Illinois.

Rockford is the third largest city in the U.S. state of Illinois, the 171st most populous city in the United States, the largest city in Illinois outside of the Chicago metropolitan area, and the city of the 148th most populous metropolitan area in the United States.

It is the county seat of Winnebago County and is located on both banks of the Rock River in far northern Illinois.

According to 2010 census data, the City of Rockford had a population of 152,871, with an outlying metropolitan area population of 348,360, which was estimated to have decreased to 150,251 and 344,623, respectively, by July 2013.

DeKalb is a city in DeKalb County, Illinois, United States.

The population was 43,862 according to the 2010 census.

The city is named after decorated German war hero Johann de Kalb, who died during the American Revolutionary War.

Electronic mail, or email, is a method of exchanging digital messages between people using digital devices such as computers and mobile phones.

Email first entered substantial use in the 1960s and by the mid-1970s had taken the form now recognized as email.

Email operates across computer networks, which today is primarily the Internet.

Some early email systems required the author and the recipient to both be online at the same time, in common with instant messaging.

Today's email systems are based on a store-and-forward model.

Email servers accept, forward, deliver, and store messages.

Neither the users nor their computers are required to be online simultaneously; they need to connect only briefly, typically to a mail server or a webmail interface, for as long as it takes to send or receive messages.