The From line contains the electronic mailing address of the person who sent the message, in the ARPA internet syntax. It may optionally also contain the full name of the person, in parentheses, after the electronic address. The electronic address is the same as the entity responsible for originating the article, unless the Sender header is present, in which case the From header might not be verified. Note that in all site and domain names, upper and lower case are considered the same, thus mark@cbosgd.UUCP, firstname.lastname@example.org, and mark@CBosgD.UUcp are all equivalent. User names may or may not be case sensitive, for example, Billy@cbosgd.UUCP might be different from BillY@cbosgd.UUCP. Programs should avoid changing the case of electronic addresses when forwarding news or mail.
RFC 822 specifies that all text in parentheses is to be interpreted as a comment. It is common in ARPANET mail to place the full name of the user in a comment at the end of the From line. This standard specifies a more rigid syntax. The full name is not considered a comment, but an optional part of the header line. Either the full name is omitted, or it appears in parentheses after the electronic address of the person posting the article, or it appears before an electronic address enclosed in angle brackets. Thus, the three permissible forms are:
From: mark@cbosgd.UUCP From: mark@cbosgd.UUCP (Mark Horton) From: Mark Horton <mark@cbosgd.UUCP>
Full names may contain any printing ASCII characters from space through tilde, with the exceptions that they may not contain parentheses "(" or ")", or angle brackets "<" or ">". Additional restrictions may be placed on full names by the mail standard, in particular, the characters comma ",", colon ":", and semicolon ";" are inadvisable in full names.