What is a FQDN?

FQDN (Fully Qualified Domain Name) is the complete name of a devive in the internet and can always be assigned to an IP address. What an FQDN address looks like is regulated in detail in the domain name system.

The following criteria are mandatory:

• The individual subsections are called “labels”.
• The labels are separated by dots.
• Each label consists of at least one and a maximum of 63 characters.
• The FQDN may not consist of more than 255 characters.
• Only numbers, letters and hyphens are allowed.
• Only one letter or digit is allowed at the beginning of a label.

See also:
Mailix Documentation: What is a Domainname Wikipedia: FQDN