14 Sep
2016
14 Sep
'16
9:21 p.m.
On Wed, Sep 14, 2016 at 5:52 PM, Lyndon Nerenberg <lyndon at orthanc.ca> wrote:
Not the standard, but a convention.
The standard is documented in RFC 5322 section 3.6.4 (and dates back to
RFC822).
I think you may mean RFC 5322 section 3.6.5, which does give a "MAY"
suggestion for the use of "Re: " at the start of the contents of the
subject field, but I'm unable to find any mention of the square
bracket or "was" convention for subject line changes within a thread
anywhere in RFC 5322, RFC 822, or even RFC 733. Aside from the "Re: "
convention, all three RFCs describe the Subject field as unstructured
text, subject to the line folding rules (defined in RFC 5322 section
2.2.3 "Long Header Fields").