Section 1 states in part:
Section 4 of this document specifies an "obsolete" syntax. There are
references in section 3 to these obsolete syntactic elements. The
rules of the obsolete syntax are elements that have appeared in
earlier versions of this specification or have previously been widely
used in Internet messages. As such, these elements MUST be
interpreted by parsers of messages in order to be conformant to this
specification. However, since items in this syntax have been
determined to be non-interoperable or to cause significant problems
for recipients of messages, they MUST NOT be generated by creators of
N.B. no mention of syntax to be changed in future revisions.
Section 4.1 states in part:
Note: The "period" (or "full stop") character (".") in obs-phrase
is not a form that was allowed in earlier versions of this or any
other specification. Period (nor any other character from
specials) was not allowed in phrase because it introduced a
parsing difficulty distinguishing between phrases and portions of
an addr-spec (see section 4.4). It appears here because the
period character is currently used in many messages in the
display-name portion of addresses, especially for initials in
names, and therefore must be interpreted properly. In the future,
period may appear in the regular syntax of phrase.
I suggest eliding the sentence in the note in section 4.1 which begins
with "In the future,". Any message generator which does not quote or
encode special characters in a phrase is and has always been non-conforming.
Such implementations should be fixed. This part of the specification should
not be changed now or in the future.