In recent years, many spam mails intending for ''One-click fraud' or ''Phishing' have been sent to many unspecified e-mail users. As one anti-spam technology, URL Blacklist based on the URLs in the spam mails is well used. However, spammers have been avoiding this technique by getting many new domains, using them only in a few spam mails, and throwing them away. In this paper, we focus on the domain registration date related to the URLs in the messages in order to improve the discrimination accuracy of spam mails. Thus, we address design and implementation of the domain registration date retrieval system which obtains domain lists from some Top Level Domain registries and records registration dates for each domain in the lists. With this system, we can retrieve the registration date of a domain by DNS.