Explanation of the Three Parts of an Email Address

The at sign is a mandatory part of an email address.

The at sign is a mandatory part of an email address.

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by Contributing Writer

An email address is a unique identifier that's the equivalent of having an online postal mailbox. Companies assign an employee a unique email address to communicate with colleagues. But not all email IDs are assigned. You can easily create your own when you sign up with an email provider for a personal email account. Whether you get an email address from your company or on your own, its layout, which comprises three parts, is the same.

Creation of the Email ID

Ray Tomlinson was a computer scientist at Bolt, Beranek and Newman. He sent the first network email in 1971. He was seeking a method for his co-workers to easily transmit messages to one another. He came up with the idea of separating the first and last parts of the email address with the "at" sign. He chose this sign because he knew it couldn’t be part of your name. As a result, no one would be confused about its purpose as a separator.


The first part of an email address is your username. It’s also called the local part. Usernames may include both numerals and letters and aren't case sensitive; a mix of uppercase letters and lowercase letters has no effect on email programs reading them. The goal is simply to make the username easy to remember when you share it. To find out how long your username can be, check with your email provider.

At Sign

The second part of an email address is the "at" sign. It looks like an “a” within a circle. You create it by holding the "Shift-2" keys on a QWERTY computer keyboard. Only one "at" sign is allowed as a separator in an email address. When you use it, you don’t add spaces around it as the spaces affect the syntax. If the email address to which you're sending doesn't actually include these spaces, you render the email address unusable.


The third part of an email address is the domain. The domain represents the company whose mail server you are using for your email service. For instance, if you have an email account from a social media site, then you have its domain name at the end of your email ID. Alternately, if you are signed up with a national ISP, then you will have its name appended after the "at" sign. Because the company is hosting your email service, the domain name is also called the host name.

About the Author

Brian Hooper has more than 10 years of editorial experience. Hooper has provided editorial services for New York publishing houses and currently writes for Fortune 500 companies in Silicon Valley. He holds a Bachelor of Science in business administration.

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