Ah, 8BITMIME. Several years ago, I looked into adding proper support to Exim, but after reading the RFCs came to the conclusion that the standard was irredeemably broken. A new 8BITMIME RFC was published since then, but still has the same flaws.
First, to do what Exim does now when 8BITMIME is "enabled", is explicitly forbidden by the RFC: >From RFC 6152, page [4]: # If a server SMTP does not support the 8-bit MIME transport extension # (either by not responding with code 250 to the EHLO command, or by # not including the EHLO keyword value 8BITMIME in its response), then # the client SMTP must not, under any circumstances, attempt to # transfer a content that contains characters outside of the US-ASCII # octet range (hex 00-7F). It gets worse from there. Not all 8-bit messages can be downconverted -- such as any "just-pass-8" non-MIME message. And some arrogant lazy imbecile MUA author, wanting a guarantee that his mailer would never have to deal with nested encodings, got a rule passed in MIME itself that said no "message/*" type object could ever have a nontrivial encoding. >From RFC 2046, page [29]: # No encoding other than "7bit", "8bit", or "binary" is permitted for # the body of a "message/rfc822" entity. The message header fields are # always US-ASCII in any case, and data within the body can still be # encoded, in which case the Content-Transfer-Encoding header field in # the encapsulated message will reflect this. Non-US-ASCII text in the # headers of an encapsulated message can be specified using the # mechanisms described in RFC 2047. This means that a valid 8-bit MIME message could contain an attached e-mail (or usenet posting) that is neither 7-bit clean nor valid MIME. The outer message would be then be impossible to convert to valid 7-bit MIME -- "7bit" CTE is insufficent, "8bit" CTE is forbidden by the transport, and QP/B64 are both barred by RFC 2047. That troubles me, because it means illegal 8bit messages leave my site whenever I forward an 8bit spam to an abuse contact. To avoid this, if Exim had an option to *enforce* 7bit, I would turn it on to ensure that I am only ever called upon to forward pure 7bit mails. ---- Michael Deutschmann <[email protected]> -- ## List details at https://lists.exim.org/mailman/listinfo/exim-users ## Exim details at http://www.exim.org/ ## Please use the Wiki with this list - http://wiki.exim.org/
