rfc1036 December 1987

2.1.1.  From

    The "From" line contains the electronic mailing address of the
    person who sent the message, in the 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 message, unless the
    "Sender" header is present, in which case the "From" header might
    not be verified.  Note that in all host and domain names, upper and
    lower case are considered the same, thus "mark@cbosgd.ATT.COM",
    "mark@cbosgd.att.com", and "mark@CBosgD.ATt.COm" are all equivalent.
    User names may or may not be case sensitive, for example,
    "Billy@cbosgd.ATT.COM" might be different from
    "BillY@cbosgd.ATT.COM".  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 Internet 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 message, or it
    appears before an electronic address which is enclosed in angle
    brackets.  Thus, the three permissible forms are:
    From: mark@cbosgd.ATT.COM
    From: mark@cbosgd.ATT.COM (Mark Horton)
    From: Mark Horton <mark@cbosgd.ATT.COM>

    Full names may contain any printing ASCII characters from space
    through tilde, except that they may not contain "(" (left
    parenthesis), ")" (right parenthesis), "<" (left angle bracket), or
    ">" (right angle bracket).  Additional restrictions may be placed on
    full names by the mail standard, in particular, the characters ","
    (comma), ":" (colon), "@" (at), "!" (bang), "/" (slash), "="
    (equal), and ";" (semicolon) are inadvisable in full names.