Today, let's define the term "fully qualified domain name," aka FQDN.

It can seem like a bit of a complicated term for a simple thing. What's an FQDN? It's a whole internet address. Sometimes it might be called a subdomain (I'm guilty of this), or an internet hostname. Think of it as the server name or host name + the domain name. For, www would be the hostname or server name, and then is the domain name. So is an FQDN, a fully qualified domain name.

If somebody asks you if you have a DMARC record for the FQDN, you would specifically enter "" in a DMARC record lookup tool. This could be called checking for a DMARC record at the FQDN level or at the subdomain level.

In the case of sending from a subdomain, like, that subdomain would also be considered an FQDN, for purposes of looking up DNS records at exactly that level of the subdomain, and also looking for specific A, MX or TXT records in DNS at exactly that level of the subdomain (, not at the top or organizational level of the domain (

Don't forget to check out the DELIVTERMS section here on Spam Resource, where we define the common terms used in email technology and deliverability.



  1. Thanks Al ! One comment maybe to add, a FQDN domain has to be ended by a dot, following your example "" would be FQDN, the final dot representing the root domain, published by the root zone served by the thirteen root server clusters :)

    1. Very technically true, though so many web-based DNS tools don't require the dot (or strip it, or don't allow it) as to probably just make it a point of confusion for people nowadays!


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