[1] RFC 4550: Internet Email to Support Diverse Service Environments (Lemonade) Profile, https://www.rfc-editor.org/rfc/rfc4550.html
[2] RFC Errata Report » RFC Editor, https://www.rfc-editor.org/errata/rfc4550
[3] RFC 5550: The Internet Email to Support Diverse Service Environments (Lemonade) Profile, https://www.rfc-editor.org/rfc/rfc5550.html