dhananjay <dhananjay(_at_)zlemail(_dot_)com> wrote:
1. 8bit MTA sending mail to 7bit MTA with Subject line in header
having 8bit characters.
That is a non-conformant message header. I think the safest thing to do
is leave it unchanged. If the 7bit MTA corrupts it or bounces it, the
fault lies with the sender for sending an invalid header. If you try to
transform the header, you are assuming that you can interpret the 80..FF
bytes, but the standards don't give you any clue how to interpret those
bytes in headers, because they're forbidden.
RFC2822 says "A field body may be composed of any US-ASCII characters,
except for CR and LF." So, such situation is quite possible.
US-ASCII is only 0..7F. A message header obeying that requirement
cannot contain bytes with the highest bit set.
2. 8bit MTA sending mail to 7bit MTA with Message body text having
8bit characters. In this case, 8bit MTA will have to encode message
body text into base64/QP and send it as attachment to original header
of message.
I see no need for an attachment. After encoding the body using
quoted-printable or base64, simply alter the Content-Transfer-Encoding
header field (which came in saying 8bit) to say quoted-printable or
base64.
AMC