http://www.rfc-editor.org/rfc/rfc6855.txt
RFC 6855: IMAP Support for UTF-8, P. Resnick, C. Newman, S. Shen2013-03-01T23:00:00-00:00This specification extends the Internet Message Access Protocol (IMAP) to support UTF-8 encoded international characters in user names, mail addresses, and message headers. This specification replaces RFC 5738.