Typically, a mail address has the following format. For further details, refer to Route–Independent Mail Addresses.
user@subdomain. ... .subdomain2.subdomain1.top-level-domain
The part of the address to the left of the @ sign is the local address. The local address can contain the following.
Information about routing with another mail transport (for example, bob::vmsvax@gateway or smallberries%mill.uucp@gateway)
An alias (for example, iggy.ignatz)
The receiving mailer is responsible for determining what the local part of the address means. For information about mailers, refer to Mailers and sendmail.
The part of the address to the right of the @ sign shows the domain levels, which is where the local address resides. A dot separates each subdomain. The domain part of the address can be an organization, a physical area, or a geographic region. Furthermore, the order of domain information is hierarchical, so the more local the subdomain, the closer the subdomain is to the @ sign.