-- seo: title: Fully Qualified Domain Name (FQDN) description: Definition of a fully qualified domain name as it relates to SendGrid. keywords: fqdn, fully qualified, dns, hostname, fully qualified domain, pqdn, tld title: Fully Qualified Domain Name (FQDN) group: glossary weight: 0 layout: page navigation: show: true
A Fully Qualified Domain Name (FQDN) is the complete domain name for a specific location in the Domain Name System (DNS) hierarchy. This is sometimes referred to as the absolute domain name.
The hierarchy can be broken down into a few parts:
The format of FQDN includes all hierarchical parts, usually [hostname].[domainname].[tld]. A mail server, for example with SendGrid, could be specified by an FQDN such as
mx.sendgrid.net as this provides the complete domain for a specific mail server. When connecting to a host the specification of a FQDN allows for the DNS to resolve the hostname to its specific IP in order to verify the connection and successfully send mail.