Domain Name Format Rules. The total length of a domain name cannot exceed 255 bytes including the dots. Internationalized Domain Name IDNIDNs are domain names that include characters used in the local representation of languages that are not written with the twenty-six letters of the basic Latin alphabet a-z.
The null label of length zero is reserved for the root zone. Domain name syntax The right-most label conveys the top-level domain. A complete domain name must have one or more subdomain names and one top-level domain name.
As with physical addresses the exact layout can vary.
Each label to the left specifies a. Each label can be up to 63 bytes long. Messages where the domain of the senders email address matches the specified value. The root of the structure is a dot.