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Fully Qualified Domain Name (FQDN)

Definition of a fully qualified domain name as it relates to SendGrid.

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:

  • Top-Level Domain (TLD), such as .edu or .com
  • Partially Qualified Domain Name (PQDN) or domain name, such as
  • Fully Qualified Domain Name (FQDN) or host name, such as

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 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.

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