Question

I would like to know what make Outlook respond to invitations send from another Outlook in the following way:

If not clear from the screenshot, Outlook in this case, asks me to confirm my attendance.

I have a program that sends an ICAL file. The ICAL file is properly sent as an attachment.
The file looks like this:

I have a program that sends an ICAL file. The ICAL file is properly sent as an attachment.

BEGIN:VCALENDAR
PRODID:TODO
VERSION:2.0
METHOD:PUBLISH
BEGIN:VEVENT
CLASS:PUBLIC
DESCRIPTION:Parameter: Value\nAuftrags-Nr.: \nVorschrift: 12\nZyklus: 12\nKommentar_1: \nKommentar_2: \nKommentar_3: 12\nPr?fstand: TODO\nV-Nr.: \nSMKL: 2\nDatum-Startzeit: TODO\nModel-Typschluessel: TODO\nCoastDowm: TODO\nBerechnen:
+TODO\nKommentar_4: TODO\nKommentar_5: TODO\nSchaltpunkttabelle: TODO\nAdd Test: TODO\nAdd Messtechnik: TODO\nKonfiguration MT: TODO\nAnwesenheit SB: TODO\n
ATTENDEE;CN=Pr?fstand; RSVP=TRUE:[e-mail]
DTSTART:20130123T131951Z
DTEND:20130123T151951Z
DTSTAMP:20130123T131956Z
LOCATION:12
ORGANIZER;CN=wurst:MAILTO:[e-mail]
PRIORITY:5
SEQUENCE:0
SUMMARY;LANGUAGE=de:Abgastest
TRANSP:OPAQUE
UID:ac4fc017-0944-4f9f-bfd1-3ffc07b486a9
X-MICROSOFT-CDO-BUSYSTATUS:FREE
X-MICROSOFT-CDO-IMPORTANCE:1
X-MICROSOFT-DISALLOW-COUNTER:TRUE
X-MS-OLK-ALLOWEXTERNCHECK:TRUE
X-MS-OLK-AUTOFILLLOCATION:FALSE
X-MS-OLK-CONFTYPE:0
BEGIN:VALARM
TRIGGER:-PT15
ACTION:DISPLAY
DESCRIPTION:Reminder
END:VALARM
END:VEVENT
END:VCALENDAR

When received in Outlook, it is seen as an Attachment:

I looked in the E-Mail properties and managed to find the following differences:
Outlooks sends the appointment in some binary file :

Content-Type: application/ms-tnef; name="winmail.dat" 
Content-Transfer-Encoding: binary

My program sends:

Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable

when I forward the “correct” appointment email (with “winmail.dat” type) from Outlook to myself and open it with mutt, I see the following, the email is composed of a few pieces:

  I     1 <no description>              [multipa/alternativ, 7bit, 8.1K]
  I     2 ├─><no description>           [text/plain, base64, utf-8, 1.4K]
  I     3 ├─><no description>           [text/html, base64, utf-8, 2.8K]
  I     4 └─><no description>           [text/calendar, base64, utf-8, 3.3K]

If I forward the same mail to mutt, again back to Outlook, it looks like this:

The content of the mail is:

Content-Type: multipart/mixed; boundary="bKyqfOwhbdpXa4YI"
Content-Disposition: inline

So, I suspect that the behavior I want to achieve is control inside the winmail.dat and not with a parameter inside the ICS file.

I must also add, my code is in JAVA, and reading about winmail.dat I found a JAVA library that creates winmail.dat. But I don’t know what property in side the binary
format will trigger this behavior.

My first question is then:

• Can I emulate this behavior using text mails only?

The second question is:

• If you can’t emulate this behavior (probably not) in plain text, does someone know the right property to set in the binary format?

Answer 1

Outlook will be perfectly happy if you will send the invitation as a MIME message with the content type of “text/calendar; method=REQUEST”.
There is no reason to use winmail.dat.