The second field of an SOA record. Informational only, it holds the E-Mail address of the person responsible for maintaining the zone. Originally formatted as if it was a Hostname, the @ symbol was an invalid character. The @ symbol was replaced by a ". ", and any "." preceding the "@" was replaced by "\.". Examples:

Relatively recently, the rules were changed to permit arbitrary characters in the Hostmaster field. Thus, the above rule is no longer necessary; however, it is still used by the majority of hostmasters, and it is assumed by many DNS validators.