Let's now examine the components of an e-mail. We need to begin with the address syntax of an e-mail. Below is a typical example of an e-mail address,
As you can see, the address has four components,
'Joe' corresponds to the 'local' segment of the address, and is the recipients username at a mail service. The '@' character is a abbreviated symbol for 'at', such as ' joe at example.com'. It connects the user to the machine. The '@' sign is also the one character of any email address which remains the same. Ray Tomlinson was responsible for proposing the use of the '@' sign in 1971.
Part 3 and 4 of an e-mail address are the hostname, 'example.com'. The hostname is typically a domain name, and the DNS system and DomainKeys are used for e-mail identification and authentication. The domain name will always remain the same for any singular e-mail service. But the 'local' part of the address will vary for every unique user created.
A domain name is broken down into two parts. For 'Example.com', 'Example' is the second-level domain (SLD), whereas, '.com' is the top-level domain (TLD). The top level domain could also be a country code top-level domain (ccTLD), such as 'Example.co.uk', the 'co.uk' part of the domain would be the ccTLD.