-The fields To:, Cc:, and/or Bcc: MAY be present. At least one recipient field
-MUST be present. These fields may use the entire syntax specified by RFC822,
-for example:
+The fields Z-To: and/or Z-Bcc: MAY be present. At least one recipient field
+MUST be present.
+
+Z-To: zot:bob@example.com, zot:alice@example.com, mailto:dave@example.com
+Z-Bcc: zot:https://example.com/profile/richard
+
+are valid entries. Adresses are comma separated and individual entries MUST NOT
+contain commas. There MAY be any number of ASCII space characters between
+entries for legibility. Header lines are terminated with a linefeed character
+(ASCII 0x0A).
+
+This specification provides the following protocol address prefixes
+for use in Z-To: or Z-Bcc: elements:
+
+zot: - normal zot delivery using webfinger or LRDD resolvable address
+dfrn: - legacy DFRN mode delivery using webfinger or LRDD resovable address
+ostatus: - normal OStatus delivery using webfinger or LRDD resovable address
+diaspora: - Diaspora network delivery using webfinger address
+facebook: - Facebook profile page URL
+twitter: - Twitter personal page URL without AJAX '#!' fragment
+mailto: - email RFC822/ESMTP address
+
+Examples:
+
+twitter:http://twitter.com/bjensen
+facebook:http://facebook.com/profile.php?id=000000001
+
+Foreign protocol addresses which have not been defined in this specification
+or future revisions of this specification and which are unknown to the
+recipient delivery process MAY be ignored.
+
+In cases where an address may contain either a webfinger or LRDD address, the
+webfinger address SHOULD be used preferentially.