• Getting rid of automatic MIME encoding conversions

    From Otto J. Makela@21:1/5 to All on Thu Nov 16 12:31:33 2023
    Once upon a time, it made sense to do automatic character set encoding conversions on the fly. With the advent of pretty much obligatory
    message DKIM signing, this option has become a bit of a liability, being
    able to check email message signature validity even after they are
    written in your mailbox is useful.

    Unfortunately on an older system I help to administer, sendmail 8.14.4
    does automatic conversions from quoted-printable to 8bit when messages
    are pushed to the local mailer, and I haven't been able to figure out
    how to completely disable these conversions.

    Messages without quoted-printable get sent correctly through, and the
    DKIM signature is correct in mailbox. Messages with quoted-printable
    (which were verified to have valid DKIM signing by an intermediate mail forwarder that added ARC headers) get converted and tagged with:

    X-MIME-Autoconverted: from quoted-printable to 8bit by HOST id MESSAGE

    Looking at http://www.sendmail.org/~ca/email/doc8.12/op-sh-5.html#sh-5.4
    I assumed that replacing the "9" with "8" in the Mlocal flags would
    rectify this. I did this by adding into sendmail.mc the lines

    MODIFY_MAILER_FLAGS(`LOCAL', `-9')dnl
    MODIFY_MAILER_FLAGS(`LOCAL', `+8')dnl

    and these caused sendmail.cf Mlocal flags to change:

    Mlocal, P=/usr/bin/procmail, F=lsDFMAw5:/|@qSPfhn9, S=EnvFromL/HdrFromL, R=EnvToL/HdrToL,
    ---
    < Mlocal, P=/usr/bin/procmail, F=lsDFMAw5:/|@qSPfhn8, S=EnvFromL/HdrFromL, R=EnvToL/HdrToL,

    But unfortunately this didn't seem to make a difference. Is this
    something hardwired into this older sendmail, or have I just
    misunderstood which part of the mailer does the conversion?

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Claus =?iso-8859-1?Q?A=DFmann?= @21:1/5 to Otto J. Makela on Fri Nov 17 01:01:53 2023
    Otto J. Makela wrote:

    Unfortunately on an older system I help to administer, sendmail 8.14.4
    does automatic conversions from quoted-printable to 8bit when messages
    are pushed to the local mailer, and I haven't been able to figure out
    how to completely disable these conversions.

    Recompile the code without setting these options:
    MIME8TO7 If non-zero, include 8 to 7 bit MIME conversions. This
    also controls advertisement of 8BITMIME in the ESMTP
    startup dialogue.
    MIME7TO8 If non-zero, include 7 to 8 bit MIME conversions.

    X-MIME-Autoconverted: from quoted-printable to 8bit by HOST id MESSAGE

    Looking at http://www.sendmail.org/~ca/email/doc8.12/op-sh-5.html#sh-5.4

    That's really old...

    I assumed that replacing the "9" with "8" in the Mlocal flags would
    rectify this. I did this by adding into sendmail.mc the lines

    8 If set, it is acceptable to send eight bit data to
    this mailer; the usual attempt to do 8->7 bit MIME
    conversions will be bypassed.

    Looks like a good idea, but are you sure the conversion happens
    when that mailer is used (maybe it happened before)? Is that mailer
    even used? Check the log entry.


    What is your setting for:
    EightBitMode=action
    [8] Set handling of eight-bit data. There
    are two kinds of eight-bit data: that de-
    clared as such using the BODY=8BITMIME ESMTP
    declaration or the -B8BITMIME command line
    flag, and undeclared 8-bit data, that is,
    input that just happens to be eight bits.
    There are three basic operations that can
    happen: undeclared 8-bit data can be auto-
    matically converted to 8BITMIME, undeclared
    8-bit data can be passed as-is without con-
    version to MIME (``just send 8''), and de-
    clared 8-bit data can be converted to 7-bits
    for transmission to a non-8BITMIME mailer.
    The possible actions are:

    s Reject undeclared 8-bit data (``strict'')
    m Convert undeclared 8-bit data to MIME (``mime'')
    p Pass undeclared 8-bit data (``pass'')

    In all cases properly declared 8BITMIME data
    will be converted to 7BIT as needed. Note:
    if an automatic conversion is performed, a
    header with the following format will be
    added:

    X-MIME-Autoconverted: from OLD to NEW by $j id $i

    where OLD and NEW describe the original for-
    mat and the converted format, respectively.



    --
    Note: please read the netiquette before posting. I will almost never
    reply to top-postings which include a full copy of the previous
    article(s) at the end because it's annoying, shows that the poster
    is too lazy to trim his article, and it's wasting the time of all readers.

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)