Recently, many spam mails associated with "One-click fraud," "Phishing," and so on have been sent to unspecified large number of e-mail users. According to some previous works, most spam mails contained some URLs whose domains were registered relatively recently, such that the age of the domain used in the URL in the messages would be a good criterion for spam mail discrimination. However, it is difficult to obtain the age or the registration date of a specific domain for each message by WHOIS service since most WHOIS services would block frequent queries. In this paper, we propose a domain registration date retrieval system, which updates zone files of some Top Level Domains (TLDs) every day, keeps track of the registration date for new domains, and works as a DNS server that replys with the registration date of the queried domain. According to the performance evaluation, the prototype system could update the registration date for all the domains of "com" TLD in two hours.Recently, many spam mails associated with "One-click fraud," "Phishing," and so on have been sent to unspecified large number of e-mail users. According to some previous works, most spam mails contained some URLs whose domains were registered relatively recently, such that the age of the domain used in the URL in the messages would be a good criterion for spam mail discrimination. However, it is difficult to obtain the age or the registration date of a specific domain for each message by WHOIS service since most WHOIS services would block frequent queries. In this paper, we propose a domain registration date retrieval system, which updates zone files of some Top Level Domains (TLDs) every day, keeps track of the registration date for new domains, and works as a DNS server that replys with the registration date of the queried domain. According to the performance evaluation, the prototype system could update the registration date for all the domains of "com" TLD in two hours.