john(_at_)interlog(_dot_)com wrote:
I use a Perl script called "premail" that can be installed as your
postproc.
Unless premail has been fixed it illegally encodes multiparts and
messages. Below is what it violates. This failure will cause your
PGP/MIME messages or other multiparts to be unreadable by many, standards
compliant mail readers.
Certain Content-Transfer-Encoding values may only be used on certain
Content-Types. In particular, it is expressly forbidden to use any
encodings other than "7bit", "8bit", or "binary" with any Content-
Type that recursively includes other Content-Type fields, notably the
"multipart" and "message" Content-Types. All encodings that are
desired for bodies of type multipart or message must be done at the
innermost level, by encoding the actual body that needs to be
encoded.
Borenstein & Freed [Page 16]
RFC 1521 MIME September 1993
NOTE ON ENCODING RESTRICTIONS: Though the prohibition against
using content-transfer-encodings on data of type multipart or
message may seem overly restrictive, it is necessary to prevent
nested encodings, in which data are passed through an encoding
algorithm multiple times, and must be decoded multiple times in
order to be properly viewed. Nested encodings add considerable
complexity to user agents: aside from the obvious efficiency
problems with such multiple encodings, they can obscure the basic
structure of a message. In particular, they can imply that
several decoding operations are necessary simply to find out what
types of objects a message contains. Banning nested encodings may
complicate the job of certain mail gateways, but this seems less
of a problem than the effect of nested encodings on user agents.
-Hal <*>