E.123 is standards-based recommendation by the International Telecommunications Union sector ITU-T, and is entitled Notation for national and international telephone numbers, e-mail addresses and Web addresses. It provides guidelines for the presentation of  telephone numbers, email addresses, and web addresses in print, on letterheads, and similar purposes.

E.123 is standards-based recommendation by the International Telecommunications Union sector ITU-T, and is entitled Notation for national and international telephone numbers, e-mail addresses and Web addresses. It provides guidelines for the presentation of  telephone numbers, email addresses, and web addresses in print, on letterheads, and similar purposes.