[1] [CITE@en[RFC 5504 - Downgrading Mechanism for Email Address Internationalization]]
([TIME[2009-11-20 22:24:55 +09:00]] 版)
<http://tools.ietf.org/html/rfc5504>

[2] [CITE@en[RFC 5983 - Mailing Lists and Internationalized Email Addresses]]
([TIME[2010-10-05 09:56:55 +09:00]] 版)
<http://tools.ietf.org/html/rfc5983>