[Tickets #13851] 8bit/binary Content-Transfer-Encoding should not be used via SMTP channel

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Ticket URL: https://bugs.horde.org/ticket/13851
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  Ticket             | 13851
  Created By         | orvos.peter at microsec.hu
  Summary            | 8bit/binary Content-Transfer-Encoding should not be
                     | used via SMTP channel
  Queue              | IMP
  Version            | 6.1.7
  Type               | Bug
  State              | Unconfirmed
  Priority           | 3. High
  Milestone          |
  Patch              |
  Owners             |
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orvos.peter at microsec.hu (2015-02-09 10:01) wrote:

Sorry, if the problem has already been solved (6.1.7 is not the most  
recent of IMP), but I couldn't find such bug reports searching your  
tickets.

Our problem is, that an ISP started to use IMP as its webmail, and  
since that point we started to receive malformed attachment contents.  
The problem is that the XML based content is attached with  
Content-Transfer-Encoding: 8bit, while it contained lines longer than  
1000 characters.

Referring to Rfc 2045 (MIME):
> 6. Content-Transfer-Encoding Header Field
>
>    Many media types which could be usefully transported via email are
>    represented, in their "natural" format, as 8bit character or binary
>    data.  Such data cannot be transmitted over some transfer protocols.
>    For example, RFC 821 (SMTP) restricts mail messages to 7bit US-ASCII
>    data with lines no longer than 1000 characters including any trailing
>    CRLF line separator.
>
>    It is necessary, therefore, to define a standard mechanism for
>    encoding such data into a 7bit short line format.  Proper labelling
>    of unencoded material in less restrictive formats for direct use over
>    less restrictive transports is also desireable.  This document
>    specifies that such encodings will be indicated by a new "Content-
>    Transfer-Encoding" header field.  This field has not been defined by
>    any previous standard.

Accordingly 8bit and binary Content-Transfer-Encodings can be used for  
ex. HTTP POSTs, however these are not to be used if the transmission  
channel is SMTP, since Rfc 821 (SMTP) allows any SMTP servers to break  
lines longer than 1000 characters or convert bodies to 7bit by will.  
Since IMP is webmail client we might state that every MIME structures  
it creates will be transferred via SMTP, therefore the usage of 8bit  
and binary transfer-encodings are contraindicated.

Thx for your kind help!