http://www.rfc-editor.org/rfc/rfc3192.txt
RFC 3192: Minimal FAX address format in Internet Mail, C. Allocchio2001-10-01T23:00:00-00:00This memo describes a simple method of encoding Global Switched Telephone Network (GSTN) addresses of facsimile devices in the local- part of Internet email addresses. [STANDARDS-TRACK]