Re: Is the "Subject" field of an e-mail an obvious example of "plain text" where no higher level protocol application is possible?

From: Philippe Verdy <>
Date: Fri, 20 Jul 2012 18:52:51 +0200

The "Subject" filed is subject to special encoding like
Quoted-Printable or Base64 using specific prefixes. This is necessary
because the MIME headers spreciying the ail encoding only applies to
the mail body but not to the headers themselves.

For this reason it is not stricly plain text.

Additionally it has specific formatting conventions related to the use
of spaces and continuation lines if needed.

Not all mail reader agents will recognize the Quoted-Printable or
Base64 signatures found in these headers (notably in: subject, from,
to), but most now actually decode them properly, privded that the
prefixes are specifying a supported charset. UTF-8 is one of thoese
charsets that will be most fequently recognized, but the ISO-8859-1 is
still much more often recognized. For Chinese, or Japanese, UTF-8 is
rarely used.

There's no way to specify a font to render the encoded characters.
When the headers contain 8-bit byte values, there's some assumption
that it will be decoded like with the encooding found or specified in
the mail body, but this is unreliable.

2012/7/20 Karl Pentzlin <>:
> Looking for an example of "plain text" which is obvious to anybody,
> it seems to me that the "Subject" field of e-mails is a good example.
> Common e-mail software lets you enter any text but gives you never
> access to any higher-level protocol. Possibly you can select the font
> in which the subject line is shown, but this is completely independent
> of the font your subject line is shown at the recipient.
> Thus, you transfer here plain text, and you can use exactly the
> characters which either Unicode provides to you, or which are PUA
> characters which you have agreed upon with the recipient before.
Received on Fri Jul 20 2012 - 12:00:46 CDT

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