[horde] Complex MIME structure and Outlook with Exchance Active Sync

Wed Sep 2 15:20:01 UTC 2015

My users complained, that some of their mails are not shown
correctly in Outlook 2013. The example mails contain a HTML body and
an ICS calendar event attachment. The MIME structure of such mails
is quiet complex:

    ... mail header
    MIME-Version: 1.0
    Content-Type: multipart/mixed;
        boundary="----=_Part_612210_854769737.1441205167596"
    ...

    ------=_Part_612210_854769737.1441205167596
    Content-Type: multipart/alternative;
        boundary="----=_Part_612211_1596854976.1441205167596"

    ------=_Part_612211_1596854976.1441205167596
    Content-Type: text/plain; charset=UTF-8
    Content-Transfer-Encoding: QUOTED-PRINTABLE
    Content-Disposition: inline

    ... plain text

    ------=_Part_612211_1596854976.1441205167596
    Content-Type: text/html; charset=UTF-8
    Content-Transfer-Encoding: QUOTED-PRINTABLE
    Content-Disposition: inline

    <html>
    ...HTML text
    </html>
    ------=_Part_612211_1596854976.1441205167596--

    ------=_Part_612210_854769737.1441205167596
    Content-Type: text/calendar; method=REQUEST
    Content-Transfer-Encoding: Base64
    Content-Disposition: attachment; filename=iCal-20150902-074607.ics

    ...Base64 coded ICS calendar event
    ------=_Part_612210_854769737.1441205167596--

For testing I set up Outlook 2013 with two identical accounts, one
with IMAP and one with Exchange Active Sync to Horde/Groupware (5.2.10).

I found, that mails in Exchange Active Sync account are changed very
much compared with the mail source on mailserver and compared with
the IMAP mail copy.

Fields like

  * headers like From, Subject ... (line breaks, character sets ...)
  * Boundary (in Content-Type header)
  * HTML content

are changed.

For instance

Content-Type: multipart/mixed;
    boundary="----=_Part_612210_854769737.1441205167596"

in the original mail file (and in IMAP) will be

Content-Type multipart/mixed; boundary="=_u0lCRt-yWhSaSeK8u9bpda_"

in Outlook using Exchange Active Sync.

My questions:

  * Does Horde transfer the complete mails 1:1 using Exchange Active
    Sync?
  * Are there any problems with Horde Active Sync and complex MIME
    structures?
  * If Horde is not the source of the problem, which additional
    tools tend to change mail headers and content. (I have a complex
    setup with Linux and Windows Antivirus programs and filters like
    Procmail.)

Greetings,
Björn