An email address is the means through which electronic mail, or email, can be received. Each address has its own mailbox hosted on a mail server. To deliver a message via email, the sender's mail server contacts the recipient's server; in turn, the latter forwards the message to the recipient's mailbox. An email address provides the information necessary for this operation. No two email addresses can be the same. Each complete address must be unique.
The user name is found on the left-most part of an email address, before the "@" symbol. It identifies a particular email account in the domain. Therefore no two addresses in a domain can have the same user name. However, email addresses in different domains can have the same user name. For example, "firstname.lastname@example.org" and "email@example.com" are both valid addresses. A user name may be a form of a person's name such as "jdoe," a nickname or alias; or it may suggest the type of correspondence for which the address is used, such as "sales" or "inquiries." A user name may consist of letters, numbers and/or special characters such as an underscore or a period, so it may mean nothing at all aside from being a user name.
The "@" symbol (read as "at") is placed between the user name and domain name, without spaces or quotes. When publishing an email address on the Web, the "@" symbol should be disguised to prevent spammers' software from identifying it as part of a valid address: "abc (at) xyz dot com." No email address is valid without this symbol.
An email address' domain is found to the right of the "@" symbol. It consists of the second- and top-level domains, separated by a dot. Typically the second-level domain is the name of the business, organization or Internet service provider that owns that domain. For example, in "firstname.lastname@example.org" the second-level domain is "xyz." Sometimes you will see third-level or fourth-level domain names, for example, "email@example.com," Each level is separated from the others by a dot.
A top-level domain is what appears right-most in an email address, after the second-level domain. For example, in "firstname.lastname@example.org," the top-level domain is ".org." Some top-level domains are generic such as .com, .net and.gov, and are referred to as gTLD or generic top-level domains. Others are country-specific such as .gov.mt (Malta), and termed ccTLD or country-code top-level domains.